randr: Scream when creating a shared pixmap fails

This seems like a problem worth screaming about.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Dave Airlie <airlied@redhat.com>

randr/rrcrtc.c

@@ -534,6 +534,7 @@ rrSetupPixmapSharing(RRCrtcPtr crtc, int width, int height,
                                       width, height, depth,
                                       x, y, rotation);
     if (spix_front == NULL) {
+        ErrorF("randr: failed to create shared pixmap\n");
         return FALSE;
     }