The HAVING clause is subject to the same rules as the SELECT list
about using aggregated and non-aggregated columns.
But this was not enforced when processing implicit grouping from
using aggregate functions.
Fixed by performing the same checks for HAVING as for SELECT.


mysql-test/r/func_group.result:
  Bug #31794: test case
mysql-test/t/func_group.test:
  Bug #31794: test case
sql/sql_select.cc:
  Bug #31794: Check HAVING in addition to SELECT list