Fix drop between shared views

Summary:
Remove trailing slash from folderUrl, too, when comparing to
the file's url (minus file name minus trailing slash). FolderUrls
like file:///home/user/Desktop/ may appear and fail comparing.

Fixes regression introduced in 07001277
(see https://phabricator.kde.org/D10729) which fixes urls like
file:///home/user/foo (if using a different folder than Desktop)
but breaks moving files from one screen to another using normal
Desktop folder.

Test Plan:
1. Use folder view, Desktop folder, more than one screen.
Create files and folders in Desktop folder and move them from one
screen to another. The Copy/Move/Link menu must not appear
and files/folders must be dropped onto the other screen.

2. Use a different folder than Desktop (the same on both screens).
Moving files/folders to another screen must work like in 1.

Reviewers: mart

Reviewed By: mart

Subscribers: amantia, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D13612

(cherry picked from commit cab9078e)