obs::source_tracker loses or duplicates references to Sources

[hassanelsherbiny]

OBS Studio Logs

N/A

Current and Expected Behavior

When obs::source_tracker is used, it should normally track and untrack all known OBS sources safely. This appears to have been broken by a commit in the past, and now needs to be fixed again.

Steps to Reproduce the Problem

1. Launch OBS Studio on an existing Scene Collection.
2. Create a new Scene Collection.
3. Add any source or scene.
4. Add a Source that uses obs::source_tracker
5. obs::source_tracker will be empty.

Any additional Information we need to know?

No response