flatpak: Fix installing flatpakrefs if the remote is already configured
When we parse a flatpakref file and find that the remote for the app is already enabled, we try to show the app from the existing remote.
This commit fixes this to actually work.
The code was already there, but instead of returning the app from the existing remote, it short circuited the flatpakref loading and returned a half-loaded flatpakref GsApp that didn't have the associated runtime correctly set up, and things went downhill from there on.
Fixes: #517 (closed)