[Cin] Use MAXCHANNELS define in mwindow.C

[Phyllis Smith]

Patch will be checked into GIT.  I read all of the email again and it seems
to at least be limited to 32 in most cases, but I find that if you use
Settings->Format, you can create more than 32 channels anyway as I set it
to 36 and it did not complain.

This is confusing though, when I load:
   http://www.gvgdevelopers.com/K2DevGuide/Clips2/NTSC_SD_DV25_colorbar.avi
into CinGG, it shows 16 audio tracks!, but ffprobe, mediainfo, and
Resources window info/details shows 8!

I am not sure that consensus was, but I see even dvd can contain up to 7.1
> audio, and even this mpeg multichannel encoder I just rediscovered had some
> support/experiments in this direction,  in 1990s)
>
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