abstract_tcp_server2: guard against accessing lock on a destroyed object

contrib/epee/include/net/abstract_tcp_server2.inl

@@ -209,14 +209,14 @@ PRAGMA_WARNING_DISABLE_VS(4355)
   bool connection<t_protocol_handler>::add_ref()
   {
     TRY_ENTRY();
-    //_dbg3("[sock " << socket_.native_handle() << "] add_ref, m_peer_number=" << mI->m_peer_number);
-    CRITICAL_REGION_LOCAL(m_self_refs_lock);
-    //_dbg3("[sock " << socket_.native_handle() << "] add_ref 2, m_peer_number=" << mI->m_peer_number);
 
     // Use safe_shared_from_this, because of this is public method and it can be called on the object being deleted
     auto self = safe_shared_from_this();
     if(!self)
       return false;
+    //_dbg3("[sock " << socket_.native_handle() << "] add_ref, m_peer_number=" << mI->m_peer_number);
+    CRITICAL_REGION_LOCAL(self->m_self_refs_lock);
+    //_dbg3("[sock " << socket_.native_handle() << "] add_ref 2, m_peer_number=" << mI->m_peer_number);
     if(m_was_shutdown)
       return false;
     m_self_refs.push_back(self);