NetPlay: Disable some UI elements when a game is running

because it makes dolphin crash, and it doesn’t make sense to change them
at runtime

Source/Core/DolphinWX/NetWindow.h

@@ -114,6 +114,7 @@ private:
 	wxCheckBox*   m_record_chkbox;
 
 	std::string   m_selected_game;
+	wxButton*     m_player_config_btn;
 	wxButton*     m_game_btn;
 	wxButton*     m_start_btn;
 	wxButton*     m_kick_btn;