message: Send null signed_block on exception
diff: @@ -454,9 +454,13 @@ namespace eosio {
  void async_get_block_num( uint32_t blocknum, L&& callback ) {
  _app_ios.post( [self = shared_from_this(), blocknum, callback]{
  auto& control = app().get_plugin<chain_plugin>().chain();
  + signed_block_ptr sblockptr;
  try {
  //ilog( "fetch block ${n}", ("n",blocknum) );
  - auto sblockptr = control.fetch_block_by_number( blocknum );
  + sblockptr = control.fetch_block_by_number( blocknum );
  + } catch ( const fc::exception& e ) {
  + edump((e.to_detail_string()));
  + }
  self->_ios.post( boost::asio::bind_executor(
  self->_strand,
  @@ -464,10 +468,6 @@ namespace eosio {
  callback(sblockptr);
  }
  ));
  -
  - } catch ( const fc::exception& e ) {
  - edump((e.to_detail_string()));
  - }
  });
  }
  