To reproduce:
1. Open a scene in a project which contains an audio clip
2. Create a timeline
3. Create a Game Object with an Audio Source component and disable it
4. Set the audio clip value for the same Game Object
5. Add the Game Object with the Audio Source to the timeline
6. Play the scene
7. Exit the play mode

Desired outcome: The editor does not crash.
Actual result: The editor crashes.

Reproduced with 2017.1.0b7, 2017.1.0f3, 2017.2.0a1, 2017.2.0b3
Not reproduced with 2017.1.0a1, 2017.1.0b6
Regression introduced in 2017.1.0b7

Stack trace:
(Unity) AudioSource::Stop
(Unity) AudioManager::StopSources
(Unity) PlayerLoopController::ExitPlayMode
(Unity) PlayerLoopController::SetIsPlaying
(Unity) Application::TickTimer
(Unity) MainMessageLoop
(Unity) WinMain
(Unity) __tmainCRTStartup
(KERNEL32) BaseThreadInitThunk
(ntdll) RtlUserThreadStart