Prepare the main looper earlier

The looper must be initialized before listing apps, to avoid the
following error:

> Can't create handler inside thread that has not called
> Looper.prepare()

Refs 283326b2f6fa3fdaeecc181f69a3a4bcd429c06a
Fixes #6165 <https://github.com/Genymobile/scrcpy/issues/6165>