Don't try to convert transfered QVariants using variant.canConvert<QVariant>()

When using QVariant as a type for a property. The generated code looks like this:

    QVariant varValue() const
    {
        const QVariant variant = propAsVariant(2);
        if (!variant.canConvert<QVariant>()) {
            qWarning() << "QtRO cannot convert the property varValue to type QVariant";
        }
        return variant.value<QVariant >();
    }

As the property is already available as a QVariant internally, there is no need to convert this again.

Trying to convert it is also a problem as a default constructed QVariant() results in a invalid QVariant and cannot be converted, which means the following error message is shown when no "valid" QVariant is send:

QtRO cannot convert the property varValue to type QVariant