Prevent SEGV in VNC server for old clients (Anthony Liguori).

Prevent SEGV in VNC server for old clients (Anthony Liguori).

If the client does not support the DesktopResize pseudo-encoding, then
vs->{width,height} may be smaller than ds->{width,height}.  dirty_row is
sized according to vs->{width,height}, not ds->{width,height}.

This patch makes sure to bound the update region to vs->{width,height} to
avoid a possible SEGV.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Reported-by: Marcelo Tosatti <mtosatti@redhat.com>

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@4502 c046a42c-6fe2-441c-8c8c-71466251a162