Prevent duplicate parsing of symmetry labels, and parsing of indices as labels.
Prevent duplicate parsing of symmetry labels, and parsing of indices as labels.

jchodera/cclib,ATenderholt/cclib,ghutchis/cclib,andersx/cclib,berquist/cclib,cclib/cclib,gaursagar/cclib,Schamnad/cclib,andersx/cclib,Schamnad/cclib,cclib/cclib,cclib/cclib,langner/cclib,langner/cclib,langner/cclib,berquist/cclib,ghutchis/cclib,ATenderholt/cclib,jchodera/cclib,gaursagar/cclib,berquist/cclib