Added event parameter to PopupMenu perform.

dist/iwmlib.pixi.js

@@ -6127,6 +6127,8 @@
         onMouseWheel(event) {
             if (this.capture(event) && this.target.onMouseWheel) {
                 this.target.onMouseWheel(event);
+            } else {
+                //console.warn('Target has no onMouseWheel callback')
             }
         }
 
@@ -6332,6 +6334,8 @@
                 }
                 if (this.target.onMouseWheel) {
                     this.target.onMouseWheel(event);
+                } else {
+                    //console.warn('Target has no onMouseWheel callback', this.target)
                 }
             }
         }
@@ -16881,7 +16885,10 @@
              * that is either passed or null.
              */
 
-            if (listeners == null) ; else if (Array.isArray(listeners)) this.listeners = listeners;
+            if (listeners == null) {
+                // Null is a valid value as the EventHandler assumes no listener is passed on purpose.
+                // This is useful, when a default parameter is passed as null.
+            } else if (Array.isArray(listeners)) this.listeners = listeners;
             else if (typeof listeners == 'function') {
                 this.listeners = [];
                 this.add(listeners);