[Openal] no context open on non-dev computers

[Garin Hiebert]

> devices=alcGetString(NULL, ALC_DEVICE_SPECIFIER)
> device=alcOpenDevice(devices);
>
> is the same as:
>
> device=alcOpenDevice(NULL);

Opening the NULL device is the equivalent of opening the device 
ALC_DEFAULT_DEVICE_SPECIFIER.  By coincidence, ALC_DEVICE_SPECIFIER will 
quite often return the default device as the first string, but that's 
not by design.

Garin