[gtk+] GDK W32: Make sure drag source window is not NULL

[Руслан Ижбулатов <ruslanizhb src gnome org>]

commit c89c19d2f982331c035a479ac5ffc2900f5aa71a
Author: Руслан Ижбулатов <lrn1986 gmail com>
Date:   Sun Nov 26 13:10:44 2017 +0000

    GDK W32: Make sure drag source window is not NULL
    
    This prevents GTK from throwing a bunch of warnings when it tries
    to get drag source window -> screen of that window -> ipc widget for that screen,
    and then tries to attach a signal handler to that widget.
    
    Specifically, this happens when we get a DnD move from another
    application.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=786509

 gdk/win32/gdkdnd-win32.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/gdk/win32/gdkdnd-win32.c b/gdk/win32/gdkdnd-win32.c
index 3e4b2e6..acc04ea 100644
--- a/gdk/win32/gdkdnd-win32.c
+++ b/gdk/win32/gdkdnd-win32.c
@@ -587,6 +587,8 @@ idroptarget_dragenter (LPDROPTARGET This,
    */
   if (current_src_context && current_src_context->context)
     g_set_object (&context->source_window, current_src_context->context->source_window);
+  else
+    g_set_object (&context->source_window, NULL); /* FIXME: Root window used to be here. Find a substitute? 
*/
 
   g_set_object (&sel_win32->target_drag_context, context);
   context->actions = GDK_ACTION_DEFAULT | GDK_ACTION_COPY | GDK_ACTION_MOVE;