[gtk/gtk-3-24: 18/20] Prevent crash if display->touch_implicit_grabs is NULL.

[John Ralls <jralls src gnome org>]

commit 9e212cd98194f4baddd821e63a2181ec24863fd3
Author: John Ralls <jralls ceridwen us>
Date:   Mon Nov 26 21:38:35 2018 +0900

    Prevent crash if display->touch_implicit_grabs is NULL.

 gdk/gdkdisplay.c | 5 +++++
 1 file changed, 5 insertions(+)
---
diff --git a/gdk/gdkdisplay.c b/gdk/gdkdisplay.c
index 1845e80de3..06d4187345 100644
--- a/gdk/gdkdisplay.c
+++ b/gdk/gdkdisplay.c
@@ -1257,6 +1257,11 @@ _gdk_display_has_touch_grab (GdkDisplay       *display,
 {
   guint i;
 
+  g_return_val_if_fail (display, NULL);
+
+  if (!display->touch_implicit_grabs)
+    return NULL;
+
   for (i = 0; i < display->touch_implicit_grabs->len; i++)
     {
       GdkTouchGrabInfo *info;