fix: usr: Fix zone filename token-parsing bug

The :iscman:`named` process could terminate unexpectedly when
processing a catalog member zone containing special characters
like '%' or '$' which could be interpreted as zone filename tokens
and trigger a case-sensitivity bug in the token-parsing code. This
has been fixed.

Closes #5849

Merge branch '5849-catz-filename-and-token-parsing-fix' into 'main'

See merge request isc-projects/bind9!11839