v0.9.5 crashes when closing a file that's playing

Hi all,

I don't know how to file bugs on the development site, so I hope reporting it here is okay.

Using the 0.9.5 pre-release, I discovered that the program crashes after these steps:
* Open app and make sure that exactly one file is loaded (one tab visible)
* Click the "Play" button to start replay
* Cllick the "close" icon on the tab of the music file

I also found that if you have two tabs open, start replay on one and then close the other, replay stops (but the program does not crash in this case).

Best, Hugo