When converting table identifiers to a new format,
some tables can be renamed twice, which subsequently
leads to the appearance of "false" auxiliary tables
belonging to another main (parent) table (which does
not actually have auxiliary tables).

This is because the table number is repeatedly added
to the aux_tables_to_rename vector inside the function
fts_check_and_drop_orphaned_tables.

To correct this error, we must add a check for the
occurrence of the table number in the aux_tables_to_rename
vector before adding a new element.

https://jira.mariadb.org/browse/MDEV-16656