function with distinct.
Loose index scan is used to find MIN/MAX values using appropriate index and
thus allow to avoid grouping. For each found row it updates non-aggregated
fields with values from row with found MIN/MAX value.
Without loose index scan non-aggregated fields are copied by end_send_group
function. With loose index scan there is no need in end_send_group and
end_send is used instead. Non-aggregated fields still need to be copied and
this was wrongly implemented in QUICK_GROUP_MIN_MAX_SELECT::get_next.
WL#3220 added a case when loose index scan can be used with end_send_group to
optimize calculation of aggregate functions with distinct. In this case
the row found by QUICK_GROUP_MIN_MAX_SELECT::get_next might belong to a next
group and copying it will produce wrong result.

Update of non-aggregated fields is moved to the end_send function from
QUICK_GROUP_MIN_MAX_SELECT::get_next.


mysql-test/r/group_min_max.result:
  Added a test case for the bug#50539.
mysql-test/t/group_min_max.test:
  Added a test case for the bug#50539.
sql/opt_range.cc:
  Bug#50539: Wrong result when loose index scan is used for an aggregate
  function with distinct.
  Update of non-aggregated fields is moved to the end_send function from
  QUICK_GROUP_MIN_MAX_SELECT::get_next.
sql/sql_select.cc:
  Bug#50539: Wrong result when loose index scan is used for an aggregate
  function with distinct.
  Update of non-aggregated fields is moved to the end_send function from
  QUICK_GROUP_MIN_MAX_SELECT::get_next.