2scomp->unsigned function generates incorrect output when given "0" to convert

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What steps will reproduce the problem?
1. Run (2scomp->unsigned 0 #) in file wav.lisp where # is any number.

What is the expected output? What do you see instead?
Expected output is 0 since there is nothing to change between 2s Complement
and unsigned values of 0.

EDIT: This error has been corrected by including 0 with the positive
numbers (where no changes are made), rather than testing if the number is
positive (where 0 is not included).

Original issue reported on code.google.com by jcor...@gmail.com on 21 Apr 2008 at 11:52