QmlDesigner: Fix expression parser for node hints

Literals seem to evaluate to an error.
If there is an error we just return the expression
which is likely a literal.

Change-Id: I38204573a31dd85de0c906954415f48ce5bace31
Reviewed-by: Alessandro Portale <alessandro.portale@qt.io>

src/plugins/qmldesigner/designercore/metainfo/nodehints.cpp

@@ -68,6 +68,11 @@ static QVariant evaluateExpression(const QString &expression, const ModelNode &m
 
     s_jsObject->setModelNode(modelNode);
     s_jsObject->setOtherNode(otherNode);
+
+    QJSValue value = s_qJSEngine->evaluate(expression);
+
+    if (value.isError())
+        return expression;
     return s_qJSEngine->evaluate(expression).toVariant();
 }