Fix previous commit by saving file;

mq.c

@@ -105,3 +105,23 @@ haggis_msg* haggis_mq_pop(haggis_mq *queue) {
     msg->prev = msg->next = NULL;
     return msg;
 }
+
+haggis_msg* haggis_mq_try_pop(haggis_mq *queue) {
+    haggis_msg *msg;
+
+    if (queue->count == 0)
+        return NULL;
+    pthread_mutex_lock(&queue->mutex);
+    queue->count--;
+    msg = queue->head;
+    if (msg->tag == EndOfArchive)
+        return msg;
+    if (queue->tail == queue->head) {
+        queue->tail = queue->head = NULL;
+    } else {
+        queue->head = queue->head->prev;
+    }
+    pthread_mutex_unlock(&queue->mutex);
+    msg->prev = msg->next = NULL;
+    return msg;
+}