NO JIRA - Clear journalSize counter

The journalSize counter should be set to 0 after KahaDB is shut down.
Usually, a store is not restarted again after stopping, but if it ever
was the value would be wrong since it wasn't reset back to 0.

activemq-kahadb-store/src/main/java/org/apache/activemq/store/kahadb/MessageDatabase.java

@@ -446,8 +446,9 @@ public abstract class MessageDatabase extends ServiceSupport implements BrokerSe
                     checkpointThread.join();
                 }
             }
-            //clear the cache on shutdown of the store
+            //clear the cache and journalSize on shutdown of the store
             storeCache.clear();
+            journalSize.set(0);
         }
     }