Cleanup ArrivalsFragment, make mListAdapter nullable
Summary:
Fixes T1312
Also fixes T1323
Test Plan:
Unclear test plan, but:
- open the arrivals, put the app in background, reopen the app, still works
- go in the favorites, open arrivals, still works
- open the map, tap a stop, click on arrivals, it still works
Reviewers: valerio.bozzolan
Reviewed By: valerio.bozzolan
Subscribers: valerio.bozzolan, Libre BusTO
Tags: Libre BusTO
Differential Revision: https://gitpull.it/D196