[gtk+/quartz-integration] Return a NULL context instead of asserting if a drag is already in progress.

[John Ralls <jralls src gnome org>]

commit cc0ba8e7c27b1cefcd129908f5cafc0981f43448
Author: John Ralls <jralls ceridwen us>
Date:   Fri Dec 31 17:05:53 2010 -0800

    Return a NULL context instead of asserting if a drag is already in progress.

 gdk/quartz/gdkdnd-quartz.c |    5 ++++-
 gtk/gtkdnd-quartz.c        |    3 +++
 2 files changed, 7 insertions(+), 1 deletions(-)
---
diff --git a/gdk/quartz/gdkdnd-quartz.c b/gdk/quartz/gdkdnd-quartz.c
index 7ba1705..fc99fd7 100644
--- a/gdk/quartz/gdkdnd-quartz.c
+++ b/gdk/quartz/gdkdnd-quartz.c
@@ -39,7 +39,10 @@ _gdk_quartz_window_drag_begin (GdkWindow *window,
                                GdkDevice *device,
                                GList     *targets)
 {
-  g_assert (_gdk_quartz_drag_source_context == NULL);
+  /* If the context isn't NULL, then we're in a drag already and the
+     calling application didn't notice. Return NULL to prevent
+     queueing up another gdk_drag_begin_idle. */
+  g_return_val_if_fail (_gdk_quartz_drag_source_context == NULL, NULL);
 
   /* Create fake context */
   _gdk_quartz_drag_source_context = g_object_new (GDK_TYPE_QUARTZ_DRAG_CONTEXT,
diff --git a/gtk/gtkdnd-quartz.c b/gtk/gtkdnd-quartz.c
index d990029..f9bec1e 100644
--- a/gtk/gtkdnd-quartz.c
+++ b/gtk/gtkdnd-quartz.c
@@ -1110,6 +1110,9 @@ gtk_drag_begin_internal (GtkWidget         *widget,
   NSWindow *nswindow;
 
   context = gdk_drag_begin (gtk_widget_get_window (widget), NULL);
+/* If we've already started a drag, gdk_drag_begin will return NULL;
+ * we don't want to do anything in that event. */
+  g_return_val_if_fail( context != NULL, NULL);
 
   info = gtk_drag_get_source_info (context, TRUE);