roundedbox: Fix a copy/paste error

This caused shadows to not be drawn in certain situations when overlayed
via a popover animation.

https://bugzilla.gnome.org/show_bug.cgi?id=746862

gtk/gtkroundedbox.c

@@ -626,7 +626,7 @@ _gtk_rounded_box_contains_rectangle (const GtkRoundedBox *box,
   if (x1 < box->box.x ||
       y1 < box->box.y ||
       x2 >= box->box.x + box->box.width ||
-      y2 >= box->box.y + box->box.width)
+      y2 >= box->box.y + box->box.height)
     return FALSE;
 
   if (x1 < box->box.x + box->corner[GTK_CSS_TOP_LEFT].horizontal &&