LibJS: Update empty TryStatement result value to undefined

It's what the spec wants us to do, although I'm not sure if it has an
observable effect anywhere, as we don't expose empty values. Let's do it
anyway.

Userland/Libraries/LibJS/AST.cpp

@@ -2013,7 +2013,7 @@ Value TryStatement::execute(Interpreter& interpreter, GlobalObject& global_objec
         }
     }
 
-    return result;
+    return result.value_or(js_undefined());
 }
 
 Value CatchClause::execute(Interpreter& interpreter, GlobalObject&) const