Load FITSFile with QUrl() to prevent empty fits field in scheduler
This MR deals with https://www.indilib.org/forum/ekos/14487-bug-reference-fit-won-t-load-on-scheduler.html. I reported this small bug two months ago and Wolfgang confirmed it. Unfortunately the correction did not not made it into 3.7.0. Perhaps it can be backported into 3.7?