FIX: added check for pyoSndServer.getIsBooted() to initPyo call

This fixes a bug arising when `pyoSndServer` was not `None` because it had been initiated earlier in the python session (by a previous instance of psychopy).  Probably nobody else noticed it because normally `core.quit()` kills the python instance, so this never arises.  In my case, we catch `core.quit()`'s call to `sys.exit(0)` and prevent it from executing, so that we can do other stuff in python after the experiment is run (including, sometimes, running another psychopy instance).