[3.1.2] update_batch not work

the issue can be resolved by reverting line 1918 of DB_query_builder
from:
if ($this->query($this->_update_batch($this->protect_identifiers($table, TRUE, NULL, FALSE), array_slice($this->qb_set, $i, $batch_size), $index)))
to:
if ($this->query($this->_update_batch($this->protect_identifiers($table, TRUE, NULL, FALSE), array_slice($this->qb_set, $i, $batch_size), $this->protect_identifiers($index))))

please push out a fix - my error log file from today was > 2000 lines its caused a few headaches over here...