compositor: Only fini region if it's not the undef region

src/compositor.c

@@ -188,6 +188,7 @@ static const pixman_region32_data_t undef_region_data;
 static void
 undef_region(pixman_region32_t *region)
 {
+	if (region->data != &undef_region_data)
 		pixman_region32_fini(region);
 	region->data = (pixman_region32_data_t *) &undef_region_data;
 }