HORNETQ-1231 make listDeliveringdMessagesAsJSON to show messages even if they are on the TX state
https://issues.jboss.org/browse/HORNETQ-1296 DeliveringCount and MessageCount can go negative Test

Test scenario added
Fixed https://issues.jboss.org/browse/HORNETQ-1296 DeliveringCount and MessageCount can go negative, prevented now

Only decremented delivery count in valid cases