Comment 2 for bug 1655689

Thread Id in general log printed as a signed number:

https://github.com/percona/percona-server/blob/5.5/sql/log.cc#L2743-L2744
      /* command_type, thread_id */
      length= my_snprintf(buff, 32, "%5ld ", (long) thread_id);

(With sizeof(long) == 4, it's enough to have 1000 connections per second and one month uptime to see negative numbers).

But pt-query-digest assuming thread_id as unsigned integer and ignoring general log entries with negative Thread Id