\phpbb\db\migration\data\v310\mysql_fulltext_drop tries to drop non existent indexes

Via https://tracker.phpbb.com/browse/PHPBB3-13221

Updating database to latest stable release

Database type :: mysqli
Previous version :: 3.1.0-dev
Installing Schema: \phpbb\db\migration\data\v310\mysql_fulltext_drop.
SQL ERROR [ mysqli ]

Can't DROP 'post_subject'; check that column/key exists [1091]

SQL

DROP INDEX post_subject ON bb304_posts

BACKTRACE

FILE: (not given by php)
LINE: (not given by php)
CALL: msg_handler()

FILE: [ROOT]/phpBB/db/driver/driver.php
LINE: 855
CALL: trigger_error()

FILE: [ROOT]/phpBB/db/driver/mysqli.php
LINE: 194
CALL: phpbb\db\driver\driver->sql_error()

FILE: [ROOT]/phpBB/db/driver/factory.php
LINE: 329
CALL: phpbb\db\driver\mysqli->sql_query()

FILE: [ROOT]/phpBB/db/tools.php
LINE: 1428
CALL: phpbb\db\driver\factory->sql_query()

FILE: [ROOT]/phpBB/db/tools.php
LINE: 1960
CALL: phpbb\db\tools->_sql_run_sql()

FILE: [ROOT]/phpBB/db/tools.php
LINE: 837
CALL: phpbb\db\tools->sql_index_drop()

FILE: (not given by php)
LINE: (not given by php)
CALL: phpbb\db\tools->perform_schema_changes()

FILE: [ROOT]/phpBB/db/migrator.php
LINE: 510
CALL: call_user_func_array()

FILE: [ROOT]/phpBB/db/migrator.php
LINE: 456
CALL: phpbb\db\migrator->run_step()

FILE: [ROOT]/phpBB/db/migrator.php
LINE: 277
CALL: phpbb\db\migrator->process_data_step()

FILE: [ROOT]/phpBB/db/migrator.php
LINE: 234
CALL: phpbb\db\migrator->try_apply()

FILE: [ROOT]/phpBB/db/migrator.php
LINE: 234
CALL: phpbb\db\migrator->try_apply()

FILE: [ROOT]/phpBB/db/migrator.php
LINE: 234
CALL: phpbb\db\migrator->try_apply()

FILE: [ROOT]/phpBB/db/migrator.php
LINE: 234
CALL: phpbb\db\migrator->try_apply()

FILE: [ROOT]/phpBB/db/migrator.php
LINE: 234
CALL: phpbb\db\migrator->try_apply()

FILE: [ROOT]/phpBB/db/migrator.php
LINE: 174
CALL: phpbb\db\migrator->try_apply()

FILE: [ROOT]/install/database_update.php
LINE: 206
CALL: phpbb\db\migrator->update()