msacm: pcm compatibility patch

[Robert Reif]

Eric Pouech wrote:

>
> I'd agree that what we don't need byte compatibility for the audio 
> conversions. We should be compatible OTOH on the size of the buffers 
> sent out (not sure it's always the case), which may cause some 
> problems in some cases.
> A+
>
>
The number of bytes read and written was the original issue
that I was investigating.  The original code actually wrote
past the end of the buffer at one point before I corrected that
a long time ago.  The Microsoft code will not read and/or
write the entire contents of the buffers under some
circumstances.  Duplicating this behavior lead to the code I
have presented.

Any audio programmer concerned about the quality of
conversions will stay as far away from Microsoft code
as possible.