When truetype fonts are use, xfs will crash on some applications like gfontsel. This is the xfs from XFree86-xfs-4.0.2-6, but might be present in earlier versions too. The offending function is xc/lib/font/FreeType/ftfuncs.c:FreeTypeFontGetGlyph which doesn't check for a valid encoding in the font.
Created attachment 9966 [details] Proposed patch
Patch applied, thanks very much for the fix! Good job!