workspaceThumbnails: Avoid access to undefined variables

If thumbnails haven't been created, they don't need to be destroyed.

https://bugzilla.gnome.org/show_bug.cgi?id=787871

diff --git a/js/ui/workspaceThumbnail.js b/js/ui/workspaceThumbnail.js
index c1b4bddc66754532263bc99d23230849a7a3bd17..1ecdd92ccb3027bb519a07d027fc8eadc79be858 100644 (file)
--- a/js/ui/workspaceThumbnail.js
+++ b/js/ui/workspaceThumbnail.js
@@ -884,6 +884,9 @@ var ThumbnailsBox = new Lang.Class({
     },
 
     _destroyThumbnails() {
+        if (this._thumbnails.length == 0)
+            return;
+
         if (this._switchWorkspaceNotifyId > 0) {
             global.window_manager.disconnect(this._switchWorkspaceNotifyId);
             this._switchWorkspaceNotifyId = 0;