Mysql server crashes because unsafe statements warning is wrongly elevated to error,
which is set the error status of Diagnostics_area of the thread in THD::binlog_query().
Yet the caller believes that binary logging shouldn't touch the status, so it will
set the status also later by my_ok(), my_error() or my_message() seperately
according to the execution result of the statement or transaction.
But the status of Diagnostics_area of the thread is allowed to set only once.

Fixed to clear the error wrongly set by binary logging, but keep the warning message.

mysql-test/suite/binlog/r/binlog_stm_ps.result:
  Change unsafe warning to NOTE level
mysql-test/suite/binlog/r/binlog_unsafe.result:
  Test case result for unsafe statements to ensure mysql sever don't crash
mysql-test/suite/binlog/t/binlog_unsafe.test:
  Test case for unsafe statements to ensure mysql sever don't crash
mysql-test/suite/rpl/r/rpl_skip_error.result:
  Change unsafe warning to NOTE level
mysql-test/suite/rpl/r/rpl_stm_loadfile.result:
  Change unsafe warning to NOTE level
mysql-test/suite/rpl/r/rpl_udf.result:
  Change unsafe warning to NOTE level
sql/sql_class.cc:
  the error status of the thread is cleared When a warning is elevated to an error
  because of unsafe warning of binary log.