Redundant calls to convert implicit record locks to explicit ones when table S-lock is held

In lock_clust_rec_read_check_and_lock there's a test on lock_table_has(trx, index->table, LOCK_X) which if fails would result in a call to lock_rec_convert_impl_to_expl<true>, which 1. has a comment "If an implicit x-lock exists on a record, convert it to an explicit one." that does not apply if a table S-lock is held and 2. does a few things such as looking up the trx_id of the record and find the trx in a global hash trx_sys. This could be called for every record scanned which affects performance