Commit 45efb161 optimized a bit too
much.  We can skip the vga_invalidate_display() in case no console
switch happened because we don't need a full redraw then.  We can *not*
skip vga_hw_update() though, because the screen content will be stale
then in case nobody else calls vga_hw_update().

Trigger: vga textmode with vnc display and no client connected.
Reported-by: NAvi Kivity <avi@redhat.com>
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>
Reviewed-by: NAlon Levy <alevy@redhat.com>
Tested-by: NAvi Kivity <avi@redhat.com>
Signed-off-by: NBlue Swirl <blauwirbel@gmail.com>