row_log_table_apply_insert_low(), row_log_table_apply_update():
When reporting the error_key_num, only count the clustered index
if it corresponds to a key in the SQL layer.
The assertion failure was probably introduced by the (incomplete)
MySQL 5.6.28 bug fix
Bug #21364096 THE BOGUS DUPLICATE KEY ERROR IN ONLINE DDL
WITH INCORRECT KEY NAME
which we are improving.
Side note: the fix was incorrectly merged to MySQL 5.7.10;
incorrect key names will continue to be reported in MySQL 5.7.
FIXME: MDEV-13668 InnoDB unnecessarily rebuilds table
FIXME: MDEV-13671 InnoDB should use case-insensitive column name comparisons
like the rest of the server
FIXME: MDEV-13640 / Properly fix MDEV-9469 'Incorrect key file' on ALTER TABLE
FIXME: investigate result difference in innodb.innodb-alter-autoinc
and ensure that MariaDB does the right thing with auto_increment_increment
and auto_increment_offset, for both ALGORITHM=INPLACE and ALGORITHM=COPY
(Oracle MySQL behaviour differs between those two).
