When the vga resolution changes, a new display surface is not allocated
immediately; instead that is deferred until the next update. However,
if we're running without a display client attached, that won't happen
and the next bitblt is likely to cause a segfault by overflowing the
display surface.
Fix by reallocating the display immediately when the resolution changes.
Tested with (Windows|Linux) x (cirrus|std) x (curses|sdl).
Changes from v1:
- fix segfault when switching virtual consoles with curses
Signed-off-by: Avi Kivity <address@hidden>