[#2198] Fix pendingSends count to decrement on rolled-back send

Author: mattrpav

activemq-broker/src/main/java/org/apache/activemq/broker/region/Queue.java

@@ -888,6 +888,7 @@ public void afterRollback() throws Exception {
             if (store != null && messageContext.message.isPersistent()) {
                 rollbackPendingCursorAdditions(messageContext.message.getMessageId());
             }
+            pendingSends.decrementAndGet();
             messageContext.message.decrementReferenceCount();
         }
     }