Add check for -m 0

[niemasd]

I wanted to make sure all pairs of sequences were compared, so I set -m 0, and the bealign step completed successfully, but then tn93 crashed. When I tried running just tn93 on the temporary files, I got the following error:

tn93: error: overlap must be positive, had: 0

tn93 is also created by you it seems, so I honestly think tn93 should allow for -m 0, but nevertheless, if an overlap of 0 is disallowed in tn93, hivtrace should check for -m to be positive before doing anything so it can error out instantly