Add thread locking to improve stability. (#585)

* Add thread locking to improve stability.

* Do not use thread locking with the ESP8266, but instead use an empty placeholder class that can be used to implement locking at a later date.

src/AsyncWebSocket.cpp

@@ -1197,6 +1197,7 @@ AsyncWebSocketMessageBuffer * AsyncWebSocket::makeBuffer(size_t size)
 {
   AsyncWebSocketMessageBuffer * buffer = new AsyncWebSocketMessageBuffer(size); 
   if (buffer) {
+    AsyncWebLockGuard l(_lock);
     _buffers.add(buffer);
   }
   return buffer; 
@@ -1207,6 +1208,7 @@ AsyncWebSocketMessageBuffer * AsyncWebSocket::makeBuffer(uint8_t * data, size_t
   AsyncWebSocketMessageBuffer * buffer = new AsyncWebSocketMessageBuffer(data, size); 
   
   if (buffer) {
+    AsyncWebLockGuard l(_lock);
     _buffers.add(buffer);
   }
 
@@ -1215,6 +1217,8 @@ AsyncWebSocketMessageBuffer * AsyncWebSocket::makeBuffer(uint8_t * data, size_t
 
 void AsyncWebSocket::_cleanBuffers()
 {
+  AsyncWebLockGuard l(_lock);
+
   for(AsyncWebSocketMessageBuffer * c: _buffers){
     if(c && c->canDelete()){
         _buffers.remove(c);