Fix display breakage when resizing the screen (v2) (Avi Kivity)

Fix display breakage when resizing the screen (v2) (Avi Kivity)

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 <avi@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@6989 c046a42c-6fe2-441c-8c8c-71466251a162