Fix a bug where "Add to Places" remains disabled

Summary:
Fix a bug where "Add to Places" doesn't get re-enabled in the context
and file menus when nothing is selected after previously selecting a
single file that is not a directory or multiple files.

Test Plan: Verify the action remains enabled when appropiate

Reviewers: Dolphin, elvisangelaccio, meven

Reviewed By: meven

Subscribers: meven, kfm-devel

Tags: Dolphin

Differential Revision: https://phabricator.kde.org/D24690