for bug #257, support NULL msg in msgs to send.

@@ -2201,11 +2201,11 @@ bool SrsConfig::get_realtime_enabled(string vhost)
     }
 
     conf = conf->get("min_latency");
-    if (!conf || conf->arg0() != "off") {
+    if (!conf || conf->arg0().empty()) {
         return SRS_PERF_MIN_LATENCY_ENABLED;
     }
 
-    return false;
+    return conf->arg0() == "on";
 }
 
 int SrsConfig::get_global_chunk_size()

@@ -688,14 +688,12 @@ int SrsRtmpConn::do_playing(SrsSource* source, SrsQueueRecvThread* trd)
         }
         
         // sendout messages, all messages are freed by send_and_free_messages().
-        if (count > 0) {
-            // no need to assert msg, for the rtmp will assert it.
-            if ((ret = rtmp->send_and_free_messages(msgs.msgs, count, res->stream_id)) != ERROR_SUCCESS) {
-                if (!srs_is_client_gracefully_close(ret)) {
-                    srs_error("send messages to client failed. ret=%d", ret);
-                }
-                return ret;
+        // no need to assert msg, for the rtmp will assert it.
+        if (count > 0 && (ret = rtmp->send_and_free_messages(msgs.msgs, count, res->stream_id)) != ERROR_SUCCESS) {
+            if (!srs_is_client_gracefully_close(ret)) {
+                srs_error("send messages to client failed. ret=%d", ret);
             }
+            return ret;
         }
         
         // if duration specified, and exceed it, stop play live.

@@ -237,7 +237,6 @@ public:
     * get packets in consumer queue.
     * @param msgs the msgs array to dump packets to send.
     * @param count the count in array, output param.
-    * @max_count the max count to dequeue, must be positive.
     */
     virtual int dump_packets(SrsMessageArray* msgs, int& count);
 #ifdef SRS_PERF_QUEUE_COND_WAIT

@@ -768,6 +768,10 @@ int SrsProtocol::do_send_messages(SrsSharedPtrMessage** msgs, int nb_msgs)
     // if cache is consumed, try another loop.
     for (int i = 0; i < nb_msgs; i++) {
         SrsSharedPtrMessage* msg = msgs[i];
+        
+        if (!msg) {
+            continue;
+        }
     
         // ignore empty message.
         if (!msg->payload || msg->size <= 0) {
@@ -1155,6 +1159,10 @@ int SrsProtocol::send_and_free_messages(SrsSharedPtrMessage** msgs, int nb_msgs,
     for (int i = 0; i < nb_msgs; i++) {
         SrsSharedPtrMessage* msg = msgs[i];
         
+        if (!msg) {
+            continue;
+        }
+        
         // check perfer cid and stream,
         // when one msg stream id is ok, ignore left.
         if (msg->check(stream_id)) {