Fix hang up and SEGV if Parse message contains a warning statement.
Fix hang up and SEGV if Parse message contains a warning statement.

  SELECT '\'';
  WARNING:  nonstandard use of \' in a string literal

If pgpool receives a warning message that is NoticeMessage('N') under
the extended query protocol, it reads a next message.

treasure-data/prestogres,treasure-data/prestogres,treasure-data/prestogres,treasure-data/prestogres,treasure-data/prestogres,treasure-data/prestogres,treasure-data/prestogres