exa/mixed: avoid copying back pixmap data when no migration took place

- When the driver handles the prepare access no copying is needed.
- Delayed pixmap creation should be fine, because it's handled by the
  first prepare access, but the exaPixmapIsOffscreen check in finish access
  will return FALSE without a driver pixmap.

Signed-off-by: Maarten Maathuis <madman2003@gmail.com>
Acked-by: Michel Dänzer <michel@daenzer.net>

exa/exa_migration_mixed.c

@@ -210,7 +210,8 @@ void exaFinishAccess_mixed(PixmapPtr pPixmap, int index)
 {
     ExaPixmapPriv(pPixmap);
 
-    if (pExaPixmap->pDamage && exaPixmapIsOffscreen(pPixmap)) {
+    if (pExaPixmap->pDamage && !pExaPixmap->offscreen &&
+	    exaPixmapIsOffscreen(pPixmap)){
 	DamageRegionProcessPending(&pPixmap->drawable);
 
 	if (index == EXA_PREPARE_DEST || index == EXA_PREPARE_AUX_DEST) {