Incorrect demand that "--noise_transcript_gtf" option be specified

[lweasel]

When simulating reads, the location of a GTF file containing noise transcript definitions should need only to be specified if background noise is being simulated (i.e. for values of "--noise-perc" other than zero). However, if "--noise-perc 0" is specified in an options file, rather than on the command line, piquant will incorrectly exit, asking that the "--noise_transcript_gtf" option be specified.

A temporary workaround is to instead specify "--noise-perc 0" on the command line.

Thank you to @hiraksarkar for finding this bug.