qprep charge groups ambivalent indexing shows no error

I made a topology in qprep using a library that had charge groups containing two H43's and no H42's, e.g. when making charge groups, I accidentally labelled H42 as H43 while also naming H43 as H43. Qprep made that topology with no errors. One should, of course, be more careful. Still, it might be useful if qprep noticed the charge groups made no sense.