surface: don't unref the current buffer on failure

If wlr_buffer_create fails, keep the previous buffer.

types/wlr_surface.c

@@ -296,15 +296,13 @@ static void surface_apply_damage(struct wlr_surface *surface) {
 		}
 	}
 
-	wlr_buffer_unref(surface->buffer);
-	surface->buffer = NULL;
-
 	struct wlr_buffer *buffer = wlr_buffer_create(surface->renderer, resource);
 	if (buffer == NULL) {
 		wlr_log(WLR_ERROR, "Failed to upload buffer");
 		return;
 	}
 
+	wlr_buffer_unref(surface->buffer);
 	surface->buffer = buffer;
 }