Core: Don't display on-screen messages via DisplayMessage until emulation has begun

Source/Core/Core/Core.cpp

@@ -140,6 +140,9 @@ std::string StopMessage(bool bMainThread, std::string Message)
 
 void DisplayMessage(const std::string& message, int time_in_ms)
 {
+	if (!IsRunning())
+		return;
+
 	// Actually displaying non-ASCII could cause things to go pear-shaped
 	for (const char& c : message)
 	{