Summary: During the SharePlugin refactoring the way the mime type was determined changed which broke opening files from the desktop.

Test Plan: I can open pkpass/jsonld files in Itinerary again

Reviewers: #kde_connect, albertvaka

Reviewed By: #kde_connect, albertvaka

Subscribers: eduisters, kdeconnect

Tags: #kde_connect

Differential Revision: https://phabricator.kde.org/D17976