If a file is removed, the file system watcher can loose its watch
on it (e.g. on Linux, inode-based).
Saving files does so "safely" by writing a temporary file, moving
the original, and moving the new file in its place, which is
triggering the issue above. That is why we need to re-register
the path in the file system watcher.

This broke in the refactoring done
by 05485071



Task-number: QTCREATORBUG-18892
Change-Id: I3b216d614b9f82e308da63c07d990e5911193655
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>