maybe core in pong_timeout_handler

[chinchilla-forest]

Hi I find a problem about pong_timeout_handler.
In file connection_impl.hpp,I see if endpoint send a ping to remote,a m_ping_timer will be create,and it will save the share_ptr of the connect.If the remote doesn't response the pong,the m_pong_timeout_handler will be called. Some case will lead to core.

Step1. create a object named WClient ,the websocketpp ppclient is a member of WClient.
Step2.set the member function(handle_pong_timeout) of WClient to ppclient as the pong_timeout_handler。
step3. create connect to a remote server,send a ping to server after connect created.
step4.the server doesn't response pong.And close the the connect
step5.the WClient receive close message,and free the WClient object.So the pong_timeout_handler is invalid.

step6. but the ppclient is not freed because it will save the share_ptr of itself when create the ping timer.

step7.the ping timer will be called because the client doesn't receive a pong from remote.
step8.so the WClient will call handle_pong_timeout,then call m_pong_timeout_handler.
but m_pong_timeout_handler is invalid, so it will generate a core file.

[chinchilla-forest]

I think it is better to check the staus if is open when call m_pong_timeout_handler.if not,may be the handler is invaild .
in file connection_impl.hpp
template
void connection::handle_pong_timeout(std::string payload,
lib::error_code const & ec)
{
if (ec) {
if (ec == transport::error::operation_aborted) {
// ignore, this is expected
return;
}

    m_elog->write(log::elevel::devel,"pong_timeout error: "+ec.message());
    return;
}

//////////////////////////////////// my advice
{
scoped_lock_type lock(m_connection_state_lock);

if (m_state != session::state::open) {
   return;
 }

}
////////////////////////////
if (m_pong_timeout_handler) {
m_pong_timeout_handler(m_connection_hdl,payload);
}
}