fix(html_custom_event): Fixed a hard-coded exception when processing custom html events. Was visible mostly when more than one handler was registered on the same event.

This is a fix for #5721

Author: carldebilly

src/Uno.UI.Runtime.WebAssembly/Xaml/UIElementWasmExtensions.cs

@@ -207,6 +207,7 @@ private static object RaiseHtmlCustomEventHandler(Delegate d, object sender, obj
 			if (d is EventHandler<HtmlCustomEventArgs> handler && args is HtmlCustomEventArgs eventArgs)
 			{
 				handler(sender, eventArgs);
+				return default;
 			}
 
 			throw new InvalidOperationException($"The parameters {args ?? "<null>"} for invoking GenericEventHandlers.RaiseEventHandler with {d} from {sender ?? "<null>"} are incorrect");