pcre: DFA operator should detect, and fail to match, empty subjects.
pcre: DFA operator should detect, and fail to match, empty subjects.

This is the fix to the unit test committed in the previous commit.

ironbee/ironbee,ironbee/ironbee,ironbee/ironbee,b1v1r/ironbee,ironbee/ironbee,b1v1r/ironbee,b1v1r/ironbee,b1v1r/ironbee,ironbee/ironbee,b1v1r/ironbee,ironbee/ironbee,ironbee/ironbee,b1v1r/ironbee,ironbee/ironbee,ironbee/ironbee,ironbee/ironbee,b1v1r/ironbee,ironbee/ironbee,ironbee/ironbee,b1v1r/ironbee,b1v1r/ironbee,b1v1r/ironbee,b1v1r/ironbee,b1v1r/ironbee