Fix the return value of aqt.main.unloadCollection() 

I finally tried the newest changes and couldn’t get it to run with exactly one profile.

I found out that the newly added (0994bd332cb0597c6275b60d42b92b4cd58791f8) return value of `unloadCollection` prevented automatic loading of a profile.

According to `aqt.main.loadProfile()` calling onSync "[will load DB](https://github.com/dae/anki/blob/master/aqt/main.py#L212)". When starting Anki, at least with exactly one profile present, `loadProfile()` depends on this being true. To make sure we do, go on loading the db after the call to `unloadCollection()` when there isn't any collection during start-up.

Maybe the simplest way to achieve that was to un-indent the `return` so `unloadCollection()` returns `True` if we start without a collection. 

(Afais the point of not returning `True` there was to signal that there is a collection still open (with unsaved changes).)