BUG Accept $limit=0 in SQLQuery->setLimit()

SQLQuery->setLimit(0, 99) should result in "SELECT ... LIMIT 0 OFFSET 1".
In fact it does "SELECT ..." without a LIMIT clause at all,
which is unexpected. This is regardless of the $offset value.
Merge pull request #2067 from chillu/pulls/sqlquery-zero-limit

BUG Accept $limit=0 in SQLQuery->setLimit()