[KInotify] Fix path matching when removing watches

Summary:
As in removeWatch the path is passed in with a trailing slash, no path
is removed.

Always add a trailing slash, as otherwise startsWith() used for parent
checks may match erroneously (i.e. "/foo/bar2" startsWith "/foo/bar",
although it is no parent).

Depends on D29190

Test Plan: ctest -R filewatch

Reviewers: Baloo, ngraham, meven

Reviewed By: meven

Subscribers: kde-frameworks-devel

Tags: Frameworks, Baloo

Differential Revision: https://phabricator.kde.org/D29189