Partially successful multi-user DROP breaks filtered replication

## Master creates a user and it exists:

MariaDB [(none)]> select user, host from mysql.user where user not in ('repl','root') order by user, host;

Empty set (0.000 sec)

MariaDB [(none)]> create user mgtest@'192.168.100.%';

Query OK, 0 rows affected (0.001 sec)

MariaDB [(none)]> select user, host from mysql.user where user not in ('repl','root') order by user, host;

+--------+---------------+

| user   | host          |

+--------+---------------+

| mgtest | 192.168.100.% |

+--------+---------------+

1 row in set (0.000 sec)

## User does not exist on replica due to replication filtering:

MariaDB [(none)]> select user, host from mysql.user where user not in ('repl','root') order by user, host;

Empty set (0.000 sec)

MariaDB [(none)]> pager grep Seconds

PAGER set to 'grep Seconds'

MariaDB [(none)]> show slave status\G

         Seconds_Behind_Master: 0

1 row in set (0.000 sec)

## Master drops valid user along with nonexistent user:

MariaDB [(none)]> drop user mgtest@'192.168.100.%', mgtest;

ERROR 1396 (HY000): Operation DROP USER failed for 'mgtest'@'%'

MariaDB [(none)]> select user, host from mysql.user where user not in ('repl','root') order by user, host;

Empty set (0.001 sec)

## Replica is broken:

Last_SQL_Error: Query caused different errors on master and slave.     Error on master: message (format)='Operation %s failed for %.256s' error code=1396 ; Error on slave: actual message='no error', error code=0. Default database: ''. Query: 'drop user mgtest@'192.168.100.%', mgtest'