This parameter was confusing in three ways:
1. It should have been named "lock" because it was used to take and
release the sound mutex, not to indicate whether it was locked.
2. In the one place this function gets called the locked argument was
set to "true", so not much point in having it optional.
3. I can't imagine that it would ever be a good idea to skip taking
and releasing the mutex.
Reviewed By: sergey
Differential Revision: https://developer.blender.org/D988
b41ce0d1b9