engine/rule_engine: Improve handling of rule targets with null target strings. (CID 1087760)
engine/rule_engine: Improve handling of rule targets with null target strings. (CID 1087760)

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