use .IsSet() instead if .Get() != NULL

Change-Id: Ia2b7a719fd398e78cc3b11d4f7b02cb81179f65f
Reviewed-on: https://review.haiku-os.org/c/haiku/+/3488
Reviewed-by: Jérôme Duval <jerome.duval@gmail.com>

Renamed HaikuDepot's home to haikudepot.

* This closes #10699. I mentioned that to stippi after his first commit
of HaikuDepot, anyway :-)