FS-7734 fixed mutex lock that should be an unlock

src/mod/applications/mod_nibblebill/mod_nibblebill.c

@@ -550,7 +550,7 @@ static switch_status_t do_billing(switch_core_session_t *session)
 	}
 
 	if (nibble_data && nibble_data->final_bill_done) {
-		switch_mutex_lock(globals.mutex);
+		switch_mutex_unlock(globals.mutex);
 		switch_log_printf(SWITCH_CHANNEL_SESSION_LOG(session), SWITCH_LOG_DEBUG, "Received heartbeat, but final bill has been committed - ignoring\n");
 		return SWITCH_STATUS_SUCCESS;
 	}