Properly terminate stuck audio thread when closing the program

[nyanpasu64]

I observed the audio thread to get stuck waiting for room to write audio, on a Windows 7 machine with an stuck audio daemon (audiodg.exe). It happens intermittently due to either bad apps, a broken audiodg.exe or APO plugin, or bad sound drivers (not sure which).

To make it work, I had to switch CSoundGen to shared_ptr ownership, which is an improvement to code maintainability in general (avoids the possibility of dangling pointers). This is a prerequisite for future refactorings.

I also fixed the audio thread burning CPU when audio isn't running (due to no audio devices, an audio initialization error, etc.).

This should be correct? I'm not confident lol