Fix adding "Create New..." menu to toolbar

Summary:
Access the object by its existing name rather than renaming it.

BUG: 405780
FIXED-IN: 19.04.1

Test Plan:
- Add {nav Create New} item to toolbar; it now works
- Verify that {nav Create New} menu and toolbar items are disabled when in the trash
- All tests still pass

Reviewers: elvisangelaccio, broulik, #dolphin, cfeck

Reviewed By: cfeck

Subscribers: cfeck, kfm-devel

Tags: #dolphin

Differential Revision: https://phabricator.kde.org/D20664