Problem: in case of failed 'show binlog events...' we don't inform that 
the log is not in use anymore. That may confuse following 'purge logs...'
command as it takes into account logs in use.

Fix: always notify that the log is not in use anymore.


mysql-test/r/rpl_rotate_logs.result:
  Fix for bug #29420: crash with show and purge binlogs
    - test result.
mysql-test/t/rpl_rotate_logs.test:
  Fix for bug #29420: crash with show and purge binlogs
    - test case.
sql/sql_repl.cc:
  Fix for bug #29420: crash with show and purge binlogs
    - always zero thd->current_linfo at the end of the mysql_show_binlog_events().