[mutter/wip/carlosg/xwayland-on-demand: 429/430] x11: protect against null MetaX11Display when looking up X11 windows

[Carlos Garnacho <carlosg src gnome org>]

commit fee2b488acd5982e294e83c611deb7296adacbe9
Author: Carlos Garnacho <carlosg gnome org>
Date:   Mon Dec 10 14:33:40 2018 +0100

    x11: protect against null MetaX11Display when looking up X11 windows
    
    This may happen after MetaX11Display destruction, as mutter's POV of
    the stack didn't catch up yet.

 src/x11/meta-x11-display.c | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/src/x11/meta-x11-display.c b/src/x11/meta-x11-display.c
index 12bbc1c55..118dd89b9 100644
--- a/src/x11/meta-x11-display.c
+++ b/src/x11/meta-x11-display.c
@@ -1567,6 +1567,8 @@ MetaWindow *
 meta_x11_display_lookup_x_window (MetaX11Display *x11_display,
                                   Window          xwindow)
 {
+  if (!x11_display)
+    return NULL;
   return g_hash_table_lookup (x11_display->xids, &xwindow);
 }