UI: Fix crash when exiting with a multitrack video stream active

[palana]

Not entirely sure if this is a good fix/the right fix, commit title etc is somewhat not final cc @tt2468, @RytoEX

Description

changes order that multitrack video output encoders and outputs are released in, to work around a crash on shutdown while the multitrack video output is active

Motivation and Context

exiting obs while the multitrack video output is active will currently cause obs to crash:
code around the crash

obs-studio/libobs/obs-encoder.c

Lines 358 to 360 in 608d3bf

	if (encoder->encoder_group->destroy_on_stop)
	obs_encoder_group_actually_destroy(
	encoder->encoder_group);

-> remove_connection calls obs_encoder_group_actually_destroy which in turn releases the last strong ref to the current encoder so encoder is an invalid pointer in remove_connection after that point, and it currently crashes in pthread_mutex_unlock(&encoder->encoder_group->mutex) for me

How Has This Been Tested?

exited obs with multitrack video output active and it no longer crashes

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 master 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.

[tt2468]

I'm not really a fan of how this relies on implicit c++ delete behavior to keep libobs from crashing. I'm looking into if it's possible to solve the issue from the libobs side.