[UnindexedFileIndexer] Skip filetime checks for new files
Summary:
In case a file is not in the index, either because it is new, or as it
should not be indexed, there is no need to retrieve the timestamps from
the file (it will be different).
Reviewers: Baloo, ngraham, astippich, poboiko
Reviewed By: Baloo, ngraham
Subscribers: kde-frameworks-devel
Tags: Frameworks, Baloo
Differential Revision: https://phabricator.kde.org/D21577