Fix bug which prevented xlet-settings from opening when clicking configure from context menu of desklet. (#13033)

Author: samw-26

js/ui/desklet.js

@@ -279,6 +279,7 @@ var Desklet = class Desklet {
     }
 
     configureDesklet(tab=0) {
+        if (typeof tab !== "number") tab = 0;
         Util.spawnCommandLine("xlet-settings desklet " + this._uuid + " -i " + this.instance_id + " -t " + tab);
     }
 }