wrann.m does not offset chan number back to 0-based indexing

[particlewizard]

rdann.m adds 1 to chan number, to comply with Matlab's 1-based indexing, but wrann.m does not subtract 1 to revert back to 0-based indexing.

A fix could be to modify line 145 of wrann.m: chan = num2chararray(chan-1, 'chan', N);