Reproduction steps:
1. Open the project
2. Open the only scene available
3. Play the scene
4. Wait for the script to finish
-Observe the console and note that none of the audio files are playing

Actual result: No errors are thrown and all externally loaded audio clips unload
Expected result: Error is thrown when unloading audio clips that were loaded externally

Reproduced on: 5.6.0a2, 5.5.0b11, 5.4.2p4, 5.4.0f1
Not reproducable on: 5.3.7f1, 5.3.6p7