fix: account for this.popup being potentially undefined in completion mousewheel listener (#5537)

* fix: account for popup being potentially undefined is mousewheel listene

Author: akoreman

src/autocomplete.js

@@ -431,7 +431,7 @@ class Autocomplete {
     }
 
     mousewheelListener(e) {
-        if (!this.popup.isMouseOver)
+        if (this.popup && !this.popup.isMouseOver)
             this.detach();
     }