reproin __dup's interfere with dcm2niix multi-file input

[yarikoptic]

I though that awkward __dup indices which I saw was solely due to adjusted in #264 handling of duplicate files -- that now it should be per each series, but I have missed now the obvious: such names as sub-sid001170_acq-25mm_magnitude__dup-011.json and sub-sid001170_acq-25mm_magnitude__dup-012.json come from the fact that the last number (1 or 2) is added upon treating multiple files being produced by dcm2niix where we simply add it to the file name (without extension). Obviously it is not exactly what I was expecting (sub-sid001170_acq-25mm_magnitude1__dup-01.json and sub-sid001170_acq-25mm_magnitude2__dup-01.json). Since those __dup files are anyways typically "discards", and if not renaming is to be done anyways, I wonder if code should somehow address it internally. Not yet sure since sounds requiring too ad-hoc of a solution, unless such "index" gets introduced explicitly within the filename template.