[gtk+] gdk: Unset the DrawingContext <-> cairo_t link on dispose

[Emmanuele Bassi <ebassi src gnome org>]

commit 0ca59bf85a13b8dc5b516d311df9c37e43566c1f
Author: Emmanuele Bassi <ebassi gnome org>
Date:   Sun Jun 12 18:55:34 2016 +0100

    gdk: Unset the DrawingContext <-> cairo_t link on dispose
    
    When disposing a GdkDrawingContext we should unset the association
    between the instance and the Cairo context; this avoids stale pointers
    in case a reference that has acquired on the Cairo context survives the
    lifetime of the GdkDrawingContext.

 gdk/gdkdrawingcontext.c |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)
---
diff --git a/gdk/gdkdrawingcontext.c b/gdk/gdkdrawingcontext.c
index c082a15..2bf4210 100644
--- a/gdk/gdkdrawingcontext.c
+++ b/gdk/gdkdrawingcontext.c
@@ -64,6 +64,12 @@ gdk_drawing_context_dispose (GObject *gobject)
 {
   GdkDrawingContext *self = GDK_DRAWING_CONTEXT (gobject);
 
+  /* Unset the drawing context, in case somebody is holding
+   * onto the Cairo context
+   */
+  if (self->cr != NULL)
+    gdk_cairo_set_drawing_context (self->cr, NULL);
+
   g_clear_object (&self->window);
   g_clear_pointer (&self->clip, cairo_region_destroy);
   g_clear_pointer (&self->cr, cairo_destroy);