Only skip surface reallocation in case the old surface was created using
qemu_alloc_display (via qemu_create_displaysurface) too, otherwise we
might end up with a DisplaySurface with the wrong backing storage.

Cc: 1658634@bugs.launchpad.net
Fixes: cd958edb
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Tested-by: Laszlo Ersek <lersek@redhat.com>
Message-id: 1485256239-12219-1-git-send-email-kraxel@redhat.com