AudioFlinger: Fix memory allocation for client-less tracks Test: Ringtone with BT Bug: 35350587 Bug: 38340117 Change-Id: If247d319d58f8f4d18b49f58ec950491871ebb2d (cherry picked from commit afb31487f3156a7284d2f0d06646c7bc00d99537) (cherry picked from commit 1159ffd5e3f832206982d45a7b030b943cc4775e)