Initialize _messageQueue_processing (#31)

Author: bkaufx

src/AsyncEventSource.h

@@ -82,7 +82,7 @@ class AsyncEventSourceClient {
 #if defined(ESP32)
  std::mutex _messageQueue_mutex;
 #else
- bool _messageQueue_processing;
+ bool _messageQueue_processing{false};
 #endif // ESP32
  LinkedList<AsyncEventSourceMessage *> _messageQueue;
  void _queueMessage(AsyncEventSourceMessage *dataMessage);