Description of problem:
if set a NULL vnc password,viewview will show authentication failed. 

Version-Release number of selected component (if applicable):


How reproducible:
# rpm -qa|grep kvm
kvm-83-246.el5
# uname -r
2.6.18-300.el5

Steps to Reproduce:
1.1./usr/libexec/qemu-kvm  -M rhel5.6.0 -m 4096 -smp
4,cores=2,threads=1,sockets=2 -cpu qemu64,vendor="AuthenticAMD",+sse2 -soundhw
all -name win7 -usbdevice tablet -rtc-td-hack -uuid
123465d2-2032-848d-bda0-de7adb149048 -boot c -drive
file=/home/rhel6.2.z-64.qcow2,if=virtio,boot=on,bus=0,unit=0,format=qcow2,cache=none,boot=on,werror=stop
-net nic,macaddr=54:52:00:27:12:23,vlan=0,model=virtio -net
tap,vlan=0,script=/etc/qemu-ifup -serial pty -parallel none -usb -balloon none
-monitor stdio -vnc :1,password

2.set NULL password
(qemu) change vnc password
Password:(input enter)
3.use vncview and password(NULL) to connect des guest 
  vncviewer 10.66.9.97:5901
  
Actual results:
authentication failed

Expected results:
vncview login des guest successful or don't allow to set a NULL password

Additional info: