appDisplay: Avoid using an undefined _swipeTracker

It might have been deleted already during shutdown by `_onDestroy()`.

Fixes: https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/6512
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2693>

diff --git a/js/ui/appDisplay.js b/js/ui/appDisplay.js
index 17afb899d1d5e530cd03f8f1c6b305fc4bfafdab..75a458f7b36ed45528d1c6f885bb60f14c565e58 100644 (file)
--- a/js/ui/appDisplay.js
+++ b/js/ui/appDisplay.js
@@ -1237,7 +1237,8 @@ var BaseAppView = GObject.registerClass({
     }
 
     vfunc_unmap() {
-        this._swipeTracker.enabled = false;
+        if (this._swipeTracker)
+            this._swipeTracker.enabled = false;
         this._disconnectDnD();
         super.vfunc_unmap();
     }