Improved encoder unpairing

[avoitenko-logitech]

Description

Unpair encoders (updated version)

Motivation and Context

This is a fix for crash with the following stack:

pthread_mutex_lock (pthread_mutex_lock.c:73)
blogva (base.c:111)
blog (base.c:119)
obs_encoder_shutdown (obs-encoder.c:553)
obs_encoder_initialize_internal (obs-encoder.c:487)
obs_encoder_initialize (obs-encoder.c:539)
initialize_audio_encoders (obs-output.c:2089)
obs_output_initialize_encoders (obs-output.c:2161)
os_gettime_ns (platform-windows.c:489)
obs_output_delay_start (obs-output-delay.c:147)
fdexp
std::_Char_traits<T>::move (xstring:119)
std::basic_string<T>::assign (xstring:3380)
obs_output_start (obs-output.c:311)
OBS_service::startStreaming (nodeobs_service.cpp:1132)

It started to happen because of incorrect attempt to fix crash in GPU encode thread.
Now I've found more proper place ho unpair encoders which is still needed to avoid operations with potentially dangling pointer.

How Has This Been Tested?

Manually, windows only.

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• My code has been run through clang-format.
• I have read the contributing document.
• My code is not on the streamlabs branch.
• The code has been tested.
• All commit messages are properly formatted and commits squashed where appropriate.
• I have included updates to all appropriate documentation.