[gtk+/gtk-3-18] popover: Avoid a crash when no relative-to widget is set

[Matthias Clasen <matthiasc src gnome org>]

commit 049eb3f769aad869341f54f8ee9544525f4293b3
Author: Matthias Clasen <mclasen redhat com>
Date:   Tue Nov 17 22:48:35 2015 -0500

    popover: Avoid a crash when no relative-to widget is set
    
    This was showing up in glade, which creates freestanding
    popovers.

 gtk/gtkpopover.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)
---
diff --git a/gtk/gtkpopover.c b/gtk/gtkpopover.c
index 0541582..c7bed7f 100644
--- a/gtk/gtkpopover.c
+++ b/gtk/gtkpopover.c
@@ -1363,6 +1363,9 @@ gtk_popover_check_invalidate_borders (GtkPopover *popover)
   GtkPositionType gap_side;
   gint tip_x, tip_y;
 
+  if (!priv->widget)
+    return;
+
   gtk_popover_get_gap_coords (popover, NULL, NULL,
                               &tip_x, &tip_y, NULL, NULL,
                               &gap_side);