Unbreak group operations by reverting previous delta which removed the

Unbreak group operations by reverting previous delta which removed the
assignment of `l' in `gr_update' to the return value of snprintf.  It
claimed to have fixed the case where snprintf returned -1--in fact, it
broke the entire routine.  Not setting `l' here causes fileupdate() to
invariably fail with EINVAL because it does its own check to assert
that the parameter isn't -1.