message: added check to prevent sigabort in net_plugin
diff: @@ -1055,7 +1055,7 @@ namespace eosio {
  void connection::fetch_timeout( boost::system::error_code ec ) {
  if( !ec ) {
  - if( !( pending_fetch->req_trx.empty( ) || pending_fetch->req_blocks.empty( ) ) ) {
  + if( pending_fetch.valid() && !( pending_fetch->req_trx.empty( ) || pending_fetch->req_blocks.empty( ) ) ) {
  my_impl->big_msg_master->retry_fetch (shared_from_this() );
  }
  }
  