MDEV-29775 : Assertion `0' failed in void Protocol::end_statement() when adding data to the MyISAM table after setting wsrep_mode=replicate_myisam

Firstly, variables wsrep_forced_binlog_format, wsrep_replicate_myisam
should not be able to set if wsrep_on=OFF.

Secondly, if wsrep_replicate_myisam=ON we allow wsrep_forced_binlog_format
to be [DEFAULT|ROW].
Signed-off-by: Julius Goryavsky <julius.goryavsky@mariadb.com>