coverity fix for event message

events/EventMessage.cpp

@@ -109,6 +109,6 @@ bool EventMessage::isClearedEventMessage() {
 	return getEvent() == INVALID_EVENT;
 }
 
-size_t EventMessage::getMinimumMessageSize() {
+size_t EventMessage::getMinimumMessageSize() const {
 	return EVENT_MESSAGE_SIZE;
 }

events/EventMessage.h

@@ -45,7 +45,7 @@ public:
 
 protected:
 	static const Event INVALID_EVENT = 0;
-	virtual size_t getMinimumMessageSize();
+	virtual size_t getMinimumMessageSize() const override;
 
 };