[mutter] wayland: Check the drag focus before processing XDND dest-side messages

[Carlos Garnacho <carlosg src gnome org>]

commit 6f64d6b0aa8e8d054183624815c605f84a985c71
Author: Carlos Garnacho <carlosg gnome org>
Date:   Mon Sep 28 14:40:53 2015 +0200

    wayland: Check the drag focus before processing XDND dest-side messages
    
    If the drag dest surface suddenly disappears, we may find ourselves
    processing an XdndPosition message that was sent before the X11 drag
    source had an opportunity to find out.
    
    In that case mutter does know, so double check before processing the
    messages.

 src/wayland/meta-xwayland-selection.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)
---
diff --git a/src/wayland/meta-xwayland-selection.c b/src/wayland/meta-xwayland-selection.c
index efc450b..3a97a40 100644
--- a/src/wayland/meta-xwayland-selection.c
+++ b/src/wayland/meta-xwayland-selection.c
@@ -1284,6 +1284,9 @@ meta_xwayland_selection_handle_client_message (MetaWaylandCompositor *compositor
       MetaWaylandDragGrab *drag_grab = compositor->seat->data_device.current_grab;
       MetaWaylandSurface *drag_focus = meta_wayland_drag_grab_get_focus (drag_grab);
 
+      if (!drag_focus)
+        return FALSE;
+
       if (event->message_type == xdnd_atoms[ATOM_DND_ENTER])
         {
           /* Bit 1 in data.l[1] determines whether there's 3 or less mimetype