The problem was due to a prior fix for BUG 9676, which limited
the rows stored in a temporary table to the LIMIT clause. This
optimization is not applicable to non-group queries with aggregate
functions. The fix disables the optimization in this case.


mysql-test/r/limit.result:
  Test case for BUG#21787
mysql-test/t/limit.test:
  Test case for BUG#21787
sql/sql_select.cc:
  If there is an aggregate function in a non-group query,
  materialize all rows in the temporary table no matter if
  there is a LIMIT clause. This is necessary, since the
  aggregate functions must be computed over all result rows,
  not just the first LIMIT rows.