MDEV-359: Fix another case where switch-off semisync could cause a race that...

MDEV-359: Fix another case where switch-off semisync could cause a race that ended with server crash.

This one was when the code releases and reaquires the lock with pthread_cond_wait() - and semisync is switched off meanwhile.

mysql-test/suite/rpl/t/rpl_mdev359.test

 --source include/have_semisync_plugin.inc
 --source include/not_embedded.inc
---source include/have_binlog_format_mixed_or_statement.inc
 --source include/have_debug_sync.inc
+--source include/have_binlog_format_mixed_or_statement.inc
 --source include/master-slave.inc
 
 # MDEV-359: There was a server crash when the code first checks if semisync

plugin/semisync/semisync_master.cc

@@ -744,6 +744,7 @@ int ReplSemiSyncMaster::commitTrx(const char* trx_wait_binlog_name,
       must have been removed from ActiveTranx.
     */
     assert(thd_killed(NULL) ||
+           !getMasterEnabled() ||
            !active_tranxs_->is_tranx_end_pos(trx_wait_binlog_name,
                                              trx_wait_binlog_pos));