Fix potential derefernce after NULL check in AudioConfigSettings.

I actually can't see how m_MaxAudioChannels, m_AudioUpmix or
m_AudioUpmixType could ever be NULL, but I think this changee is what
the original author intended.  Fixes Coverity 700422.
Comment out unused variable in AudioConfigSettings.

One less warning.  jya, I only commented out bDTS instead of removing
it entirely in case you have an intended use for it in the future.