Remove pf.path() from container before the reference got screwed up by it.remove()

Summary:
With a75db7aedfcd356b027774e0dc156c334d4cb869 I introduced a crash when removing a watched
directory. The Problem is that it.remove() invalidates the reference to PendingFile which
leads to a crash... :(
I found no bugreport about this on bugs.kde.org until now.

Test Plan: Remove a directory, baloo should never crash when removing a watched directory

Reviewers: broulik

Reviewed By: broulik

Subscribers: Frameworks

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D7926