[gtk/wip/carlosg/tablet-invalid-reads-master] gdk: Avoid poking possibly freed memory

[Carlos Garnacho <carlosg src gnome org>]

commit 075c77325b051e9257d19ab31886755507d599dc
Author: Carlos Garnacho <carlosg gnome org>
Date:   Tue Oct 8 17:56:10 2019 +0200

    gdk: Avoid poking possibly freed memory
    
    The event may end up freed after delivery, ensure to keep a ref in order
    to emit the matching emulated crossed event matching a proximity event.
    
    Closes: https://gitlab.gnome.org/GNOME/gtk/issues/2157

 gdk/wayland/gdkdevice-wayland.c | 4 ++++
 1 file changed, 4 insertions(+)
---
diff --git a/gdk/wayland/gdkdevice-wayland.c b/gdk/wayland/gdkdevice-wayland.c
index 7a7031d882..1b66f37b3a 100644
--- a/gdk/wayland/gdkdevice-wayland.c
+++ b/gdk/wayland/gdkdevice-wayland.c
@@ -3327,6 +3327,8 @@ gdk_wayland_tablet_flush_frame_event (GdkWaylandTabletData *tablet,
   if (!event)
     return;
 
+  g_object_ref (event);
+
   switch ((guint) event->any.type)
     {
     case GDK_MOTION_NOTIFY:
@@ -3367,6 +3369,8 @@ gdk_wayland_tablet_flush_frame_event (GdkWaylandTabletData *tablet,
     emulate_crossing (event->any.surface, NULL,
                       tablet->master, GDK_ENTER_NOTIFY,
                       GDK_CROSSING_NORMAL, time);
+
+  g_object_unref (event);
 }
 
 static GdkEvent *