b=414095, serious win32 repaint/clipping issues, r=sleepy

gfx/cairo/cairo/src/cairo-win32-surface.c

@@ -2052,7 +2052,7 @@ _cairo_win32_save_initial_clip (HDC hdc, cairo_win32_surface_t *surface)
 
     if (clipBoxType == COMPLEXREGION) {
 	surface->initial_clip_rgn = CreateRectRgn (0, 0, 0, 0);
-	if (GetClipRgn (hdc, surface->initial_clip_rgn) == -1) {
+	if (GetClipRgn (hdc, surface->initial_clip_rgn) <= 0) {
 	    /* this should never happen */
 	    DeleteObject(surface->initial_clip_rgn);
 	    surface->initial_clip_rgn = NULL;