Fix HTTP Server stop to allow it to be safe to call multiple times
Fix HTTP Server stop to allow it to be safe to call multiple times

mitchellwills/async_web_server_cpp,WPI-RAIL/async_web_server_cpp,mitchellwills/async_web_server_cpp,WPI-RAIL/async_web_server_cpp,mitchellwills/async_web_server_cpp,WPI-RAIL/async_web_server_cpp