In mathgen.pl::generate_bibtex, the compute_re can be moved out of the loop

[m00shm00sh]

compute_re can be moved out of the loop by setting $rules->{"CITE_LABEL_GIVEN"} to 1 before the loop, recomputing re, then inside the loop setting the hashtable entry to [$clabel].

This has been tested in a local build to not introduce regressions and the issue exists mostly for the sake of attaching to a pull request.