Don't crash in DND when the X server doesn't support SHAPE

Reported in bug 612768
(cherry picked from commit 996541d096)

gdk/x11/gdkwindow-x11.c

@@ -4606,11 +4606,15 @@ _xwindow_get_shape (Display *xdisplay,
   gint rn, ord, i;
 
   shape = NULL;
+  rn = 0;
 
   xrl = XShapeGetRectangles (xdisplay,
 			     window,
 			     shape_type, &rn, &ord);
 
+  if (xrl == NULL)
+    return NULL; /* XShape not supported */
+
   if (rn == 0)
     return gdk_region_new (); /* Empty */
 
@@ -4663,8 +4667,7 @@ _gdk_windowing_get_shape_for_mask (GdkBitmap *mask)
   region = _xwindow_get_shape (GDK_DISPLAY_XDISPLAY (display),
                                window, ShapeBounding);
 
-  XDestroyWindow (GDK_DISPLAY_XDISPLAY (display),
-		  window);
+  XDestroyWindow (GDK_DISPLAY_XDISPLAY (display), window);
 
   return region;
 }