bugfix: Fix illegal audio state exception.

Not quite sure how to replicate this bug but I see a lot of it in the
crash reports. Bug seems to have been introduced in commit
6cfff95c269a3aad48a138d1cd5fcb81e383b4b9 after cutting and pasting SDL2
Android example code.

The bug is that a stale audio thread must quit before initializing a
new one, and some startup code should be surrounded by try/catch.  Bug
fixed mostly by reverting the cut/paste code in CoreInterfaceNative.