The square sound channels will be out of spec when playing on the lowest octave. The result is a rather ugly noise. This bug makes a rather subtle appearance if the channel remapping is accurate, but it becomes quite obvious in the SQ4 intro with the current implementation. This commit turns off the channel when trying to play out of spec.
This fixes two evalutation issues specific to the MSVC x64 release build (other builds worked fine).
This also fixes an analysis warning regarding my use of the span code.