[tagsaction] Don't crash on multiple files
Summary:
Tagging multiple files is not supported and thus we never create m_metadata for it. However, we start the tags listing and as soon as tags are found m_metadata is accesses which results in a crash.
This patch delays the tags listing until m_metadata has been initialized
BUG: 401733
Test Plan: Select multiple files in Dolphin, right click -> no crash
Reviewers: elvisangelaccio
Reviewed By: elvisangelaccio
Subscribers: Baloo
Tags: Baloo
Differential Revision: https://phabricator.kde.org/D20361