moc: Fix parsing of operator<

moc would skip the 'operator' keyword as unknown and try to parse a type again
but as it sees the '<' it looks for the corresponding '>' which does not exist
types can't start with '<' anyway, so return an invalid type and continue
parsing as usual

Task-number: QTBUG-36834

Change-Id: If3d27076ef9947abf8c57c594713eece9334d0b0
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@digia.com>