A failed REVOKE statement is logged with error=0, thus causing
the slave to stop. The slave should not stop as this was an
expected error. Given that the execution failed on the master as
well the error code should be logged so that the slave can replay
the statement, get an error and compare with the master's
execution outcome. If errors match, then slave can proceed with
replication, as the error it got, when replaying the statement,
was expected.

In this particular case, the bug surfaces because the error code
is pushed to the THD diagnostics area after writing the event to
the binary log. Therefore, it would be logged with the THD
diagnostics area clean, hence its error code would not contain 
the correct code.

We fix this by moving the error reporting ahead of the call to
the routine that writes the event to the binary log.