fix match token-level condition: immediately terminate and return empty match result when curr pos is outside sent

This is a workaround for lovely boost 1.48 incompatibility causing compile errors on assignment to StrSet from a temporary StrSet, see https://svn.boost.org/trac/boost/ticket/6167 for more details.

It would create one only if top-level parse_match_operator
parser rule had been used. Now it creates it within
match_rule_operator parser rule, so it works for parse_wccl_file
as well.