[FIX] Error formatting subject labels for group reports
[FIX] Error formatting subject labels for group reports

This bugfix closes #551.

With thanks to @jvarada and A. Dufford for reporting this.

oesteban/mriqc,oesteban/mriqc,poldracklab/mriqc,oesteban/mriqc,oesteban/mriqc,poldracklab/mriqc,poldracklab/mriqc,poldracklab/mriqc