Ensure to store resource uri without a trailing slash

Summary:
Some apps may send resource such as

/home/me/Documents/

When others, can send the uri without the trailing slash

/home/me/Documents

This prevents matching of URI in requests.
And the trailing slash prevents KFileItem build from resources to have a proper filename

Reviewers: ivan, Frameworks

Reviewed By: ivan

Subscribers: kde-frameworks-devel

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D26415