audioflinger: fix OutputTrack initial check

Call initCheck() on newly created OutputTrack in
DuplicatingThread::addOutputTrack() to make sure that
the track is successfully attached to the AudioMixer.

Also make invalid track name always fatal in AudioMixer::deleteTrackName().

Bug: 29953737
Change-Id: I47f2517bd53de940e125391de99c40611ad0fc9d