The change from MDEV-29465 exposed a flaw in replace_column_table
where again we were not properly updating the column-level bits.

replace_table_table was changed in MDEV-29465 to properly update
grant_table->init_cols, however replace_column_table still only
modified grant_column->rights when the GRANT_COLUMN already existed.

This lead to a missmatch between GRANT_COLUMN::init_rights and
GRANT_COLUMN::rights, *if* the GRANT_COLUMN already existed.

As an example:

GRANT SELECT (col1) ...
Here:
For col1
GRANT_COLUMN::init_rights and GRANT_COLUMN::rights are set to 1 (SELECT) in
replace_column_table.

GRANT INSERT (col1) ...
Here, without this patch GRANT_COLUMN::init_rights is still 1 and
GRANT_COLUMN::rights is 3 (SELECT_PRIV | INSERT_PRIV)

Finally, if before this patch, one does:

REVOKE SELECT (col1) ...

replace_table_table will see that init_rights loses bit 1 thus it
considers there are no more rights granted on that particular table.

This prompts the whole GRANT_TABLE to be removed via the first revoke,
when the GRANT_COLUMN corresponding to it should still have init_rights == 2.

By also updating replace_column_table to keep init_rights in sync
properly, the issue is resolved.

Reviewed by <serg@mariadb.com>