dri2: Always re-generate front buffer information when asked for it.

Otherwise we might keep stale cached information, e.g. after the driver
performed page flipping.

This is part of the fix for
https://bugs.freedesktop.org/show_bug.cgi?id=35452 .

Signed-off-by: Michel Dänzer <daenzer@vmware.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@nokia.com>
Reviewed-by: Mario Kleiner <mario.kleiner@tuebingen.mpg.de>
Signed-off-by: Keith Packard <keithp@keithp.com>

hw/xfree86/dri2/dri2.c

@@ -377,6 +377,7 @@ allocate_or_reuse_buffer(DrawablePtr pDraw, DRI2ScreenPtr ds,
     int old_buf = find_attachment(pPriv, attachment);
 
     if ((old_buf < 0)
+	|| attachment == DRI2BufferFrontLeft
 	|| !dimensions_match
 	|| (pPriv->buffers[old_buf]->format != format)) {
 	*buffer = (*ds->CreateBuffer)(pDraw, attachment, format);