concat: fix locking in SEGMENT event handler
concat->current_start_offset needs the lock taken for safe access, as it can be accessed from outside of the streaming thread, eg in release_pad.
An early break is also added for an error case.
concat->current_start_offset needs the lock taken for safe access, as it can be accessed from outside of the streaming thread, eg in release_pad.
An early break is also added for an error case.