[Folder view] Don't create a rubberband when dragging during a rename

Summary:
BUG: 415816
FIXED-IN: 5.18.0

Test Plan:
Rename an item on the desktop
Start a drag within the text area
While dragging, move the cursor out of the text area
Other filed no longer get selected by a rubberband

Reviewers: hein, #plasma

Reviewed By: hein, #plasma

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D26482