Description of problem:
Occasionally, unplugging a monitor causes X to crash.

Version-Release number of selected component (if applicable):
xorg-x11-server-Xorg-1.9.99.1-2.20101201.fc15.x86_64
xorg-x11-drv-intel-2.13.901-5.fc15.x86_64
kernel-2.6.35.10-74.fc14.x86_64

How reproducible:
Sometimes. It seems to happen only when the X server has been up for a while.

Steps to Reproduce:
1. plug an external monitor to the VGA port of a laptop
2. turn on the VGA output and turn off the internal LVDS
3. unplug the monitor
4. repeat until X crashes, opening more windows

Additional info:

Crash happens because scrn->currentMode is NULL:

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459     if (full_height && INTEL_INFO(intel)->gen < 40)
465                 MI_LOAD_SCAN_LINES_DISPLAY_PIPEA;
466             if (full_height && INTEL_INFO(intel)->gen >= 40)
467                 event = MI_WAIT_FOR_PIPEA_SVBLANK;
468     } else {
469             event = MI_WAIT_FOR_PIPEB_SCAN_LINE_WINDOW;
470             load_scan_lines_pipe =
471                 MI_LOAD_SCAN_LINES_DISPLAY_PIPEB;
472             if (full_height && INTEL_INFO(intel)->gen >= 40)
473                 event = MI_WAIT_FOR_PIPEB_SVBLANK;
474     }
475
476 --> if (scrn->currentMode->Flags & V_INTERLACE) {
477             /* DSL count field lines */
478             y1 /= 2;
479             y2 /= 2;
480     }
481
482     BEGIN_BATCH(5);
483     /*
484      * The documentation says that the LOAD_SCAN_LINES

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#0  0x00007f1a8a802599 in I830DRI2CopyRegion (drawable=0x3674820, pRegion=0x0, destBuffer=<value optimized out>, sourceBuffer=<value optimized out>) at intel_dri.c:476
        box = <value optimized out>
        crtcbox = {x1 = 0, y1 = 0, x2 = 1920, y2 = 1080}
        y1 = 26
        pipe = <value optimized out>
        crtc = <value optimized out>
        full_height = <value optimized out>
        y2 = 27
        event = 2
        load_scan_lines_pipe = 0
        srcPrivate = <value optimized out>
        dstPrivate = <value optimized out>
        screen = <value optimized out>
        scrn = 0x15ca8e0
        intel = 0x15cae60
        src = 0x341c6b0
        dst = 0x3674820
        pCopyClip = <value optimized out>
        gc = 0x3154740
        __FUNCTION__ = "I830DRI2CopyRegion"
        __PRETTY_FUNCTION__ = "I830DRI2CopyRegion"
#1  0x00007f1a8aa30010 in DRI2CopyRegion (pDraw=0x3674820, pRegion=0x37cd140, dest=0, src=1) at dri2.c:617
        ds = 0x15d7600
        pPriv = <value optimized out>
        pDestBuffer = <value optimized out>
        pSrcBuffer = <value optimized out>
        i = <value optimized out>
#2  0x00007f1a8aa31e80 in ProcDRI2CopyRegion (client=0x36fa870) at dri2ext.c:325
        rep = {type = 0 '\000', pad1 = 0 '\000', sequenceNumber = 0, length = 0, pad2 = 4620207, pad3 = 0, pad4 = 3377022192, pad5 = 32767, pad6 = 4967614, pad7 = 0}
        status = <value optimized out>
        stuff = 0x34f7c70
        pDrawable = 0x3674820
        pRegion = 0x37cd140
#3  ProcDRI2Dispatch (client=0x36fa870) at dri2ext.c:566
        stuff = <value optimized out>
#4  0x000000000042d539 in Dispatch () at dispatch.c:431
        clientReady = 0x3307160
        result = <value optimized out>
        client = 0x36fa870
        nready = 0
        icheck = 0x7e78d0
        start_tick = 7660
#5  0x00000000004211ca in main (argc=<value optimized out>, argv=0x7fffc94946d8, envp=<value optimized out>) at main.c:287
        i = <value optimized out>
        alwaysCheckForInput = {0, 1}

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scrn->currentMode = {driverVersion = 4000, driverName = 0x7f1a8a81a621 "intel", pScreen = 0x15db1a0, scrnIndex = 0, configured = 1, origIndex = 0, imageByteOrder = 0, bitmapScanlineUnit = 32, bitmapScanlinePad = 32, bitmapBitOrder = 0, numFormats = 0, formats = {{depth = 0 '\000', bitsPerPixel = 0 '\000', scanlinePad = 0 '\000'}, {depth = 0 '\000', bitsPerPixel = 0 '\000', scanlinePad = 0 '\000'}, {depth = 0 '\000', bitsPerPixel = 0 '\000', scanlinePad = 0 '\000'}, {depth = 0 '\000', bitsPerPixel = 0 '\000', scanlinePad = 0 '\000'}, {depth = 0 '\000', bitsPerPixel = 0 '\000', scanlinePad = 0 '\000'}, {depth = 0 '\000', bitsPerPixel = 0 '\000', scanlinePad = 0 '\000'}, {depth = 0 '\000', bitsPerPixel = 0 '\000', scanlinePad = 0 '\000'}, {depth = 0 '\000', bitsPerPixel = 0 '\000', scanlinePad = 0 '\000'}}, fbFormat = {depth = 24 '\030', bitsPerPixel = 32 ' ', scanlinePad = 32 ' '}, bitsPerPixel = 32, pixmap24 = Pix24DontCare, depth = 24, depthFrom = X_DEFAULT, bitsPerPixelFrom = X_PROBED, weight = {red = 8, green = 8, blue = 8}, mask = {red = 16711680, green = 65280, blue = 255}, offset = {red = 16, green = 8, blue = 0}, rgbBits = 8, gamma = {red = 1, green = 1, blue = 1}, defaultVisual = 4, maxHValue = 0, maxVValue = 0, virtualX = 1920, virtualY = 1080, xInc = 0, virtualFrom = X_PROBED, displayWidth = 1920, frameX0 = 0, frameY0 = 0, frameX1 = 1279, frameY1 = 799, zoomLocked = 0, modePool = 0x0, modes = 0x0, currentMode = 0x0, confScreen = 0x15b6520, monitor = 0x15b6600, display = 0x15d3220, entityList = 0x15bd420, numEntities = 1, widthmm = 0, heightmm = 0, xDpi = 96, yDpi = 96, name = 0x7f1a8a81a621 "intel", driverPrivate = 0x15cae60, privates = 0x15c2a30, drv = 0x15c9e80, module = 0x15c9ee0, colorKey = 0, overlayFlags = 0, chipset = 0x7f1a8a81a6ed "Arrandale", ramdac = 0x0, clockchip = 0x0, progClock = 1, numClocks = 0, clock = {0 <repeats 128 times>}, videoRam = 262144, biosBase = 0, memPhysBase = 0, fbOffset = 0, domainIOBase = 0, memClk = 0, textClockFreq = 0, flipPixels = 0, options = 0x0, chipID = 0, chipRev = 0, vtSema = 1, silkenMouse = 1, clockRanges = 0x0, adjustFlags = 0, preferClone = 0, reservedInt = {0 <repeats 15 times>}, entityInstanceList = 0x15bd440, vgaDev = 0x15c0150, reservedPtr = {0x0 <repeats 14 times>}, Probe = 0, PreInit = 0x7f1a8a7ec720 <I830PreInit>, ScreenInit = 0x7f1a8a7eb8a0 <I830ScreenInit>, SwitchMode = 0x53ec40 <xf86CursorSwitchMode>, AdjustFrame = 0x52fd70 <xf86XVAdjustFrame>, EnterVT = 0x7f1a8b0847e0 <glxDRIEnterVT>, LeaveVT = 0x7f1a8b084730 <glxDRILeaveVT>, FreeScreen = 0x7f1a8a7eb6c0 <I830FreeScreen>, ValidMode = 0x7f1a8a7eb640 <I830ValidMode>, EnableDisableFBAccess = 0x53f0d0 <xf86CursorEnableDisableFBAccess>, SetDGAMode = 0x527d40 <xf86SetDGAMode>, ChangeGamma = 0x490340 <xf86RandR12ChangeGamma>, PointerMoved = 0x491410 <xf86RandR12PointerMoved>, PMEvent = 0x7f1a8a7eb500 <I830PMEvent>, DPMSSet = 0x489460 <xf86DPMSSet>, LoadPalette = 0, SetOverscan = 0, DriverFunc = 0, reservedFuncs = {0 <repeats 11 times>}}