mac-capture: Don't read channels for disconnected audio device

[jcm93]

Description

When getting CoreAudio properties for an audio device source on macOS, make sure the source is active and initialized before trying to read channel information.

Motivation and Context

If we had an audio device source on macOS, and that device was subsequently disconnected from the machine, OBS would uninitialize the source, freeing the data associated with the audio channels. libobs however would still see the channel layout information, and when trying to get the source properties, would read from the previously freed channel data.

Fixes #11432, https://obsproject.com/forum/threads/crash-on-macos.181702/

Some other issues still abound in this code, and it is somewhat due for improvement, but for now, important to fix what is actually crashing.

How Has This Been Tested?

Tested locally on macOS 15.1; first reproduced the crash per the instructions in #11432. With the patch applied, the crash no longer occurs.

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.