mqueue: decrease number of items when size limit is reached

- proper counting of intems in the queue
- patch by Denis Chukhryaev

modules/mqueue/mqueue_api.c

@@ -343,6 +343,7 @@ int mq_item_add(str *qname, str *key, str *val)
 			mh->ilast = NULL;
 		else
 			mh->ifirst->prev = NULL;
+		mh->csize--;
 		shm_free(mi);
 	}
 	lock_release(&mh->lock);