constraints: Don't early out of custom rule if window can't fit

Still go through the rules. For example a tall menu might still be
positioned better, and/or shrunk to a better size if applicable.

https://bugzilla.gnome.org/show_bug.cgi?id=771297

src/core/constraints.c

@@ -784,10 +784,6 @@ constrain_custom_rule (MetaWindow         *window,
   if (!placement_rule)
     return TRUE;
 
-  if (!meta_rectangle_could_fit_rect (&info->work_area_monitor,
-                                      &info->current))
-    return TRUE;
-
   meta_rectangle_intersect (&info->current, &info->work_area_monitor,
                             &intersection);