Queries optimized with GROUP_MIN_MAX didn't cleanup KEYREAD
optimization properly. As a result subsequent queries may
return incomplete rows (fields are initialized to default
values).

mysql-test/r/group_min_max.result:
  A test case for BUG#49902.
mysql-test/t/group_min_max.test:
  A test case for BUG#49902.
sql/opt_range.cc:
  Refactor of KEYREAD optimization switch so that KEYREAD
  handler state is in sync with st_table::key_read flag.
  
  All SQL code is supposed to switch KEYREAD optimization
  via st_table::set_keyread().
sql/opt_sum.cc:
  Refactor of KEYREAD optimization switch so that KEYREAD
  handler state is in sync with st_table::key_read flag.
  
  All SQL code is supposed to switch KEYREAD optimization
  via st_table::set_keyread().
sql/sql_select.cc:
  Refactor of KEYREAD optimization switch so that KEYREAD
  handler state is in sync with st_table::key_read flag.
  
  All SQL code is supposed to switch KEYREAD optimization
  via st_table::set_keyread().
sql/sql_update.cc:
  Refactor of KEYREAD optimization switch so that KEYREAD
  handler state is in sync with st_table::key_read flag.
  
  All SQL code is supposed to switch KEYREAD optimization
  via st_table::set_keyread().
sql/table.cc:
  Refactor of KEYREAD optimization switch so that KEYREAD
  handler state is in sync with st_table::key_read flag.
  
  All SQL code is supposed to switch KEYREAD optimization
  via st_table::set_keyread().
sql/table.h:
  Refactor of KEYREAD optimization switch so that KEYREAD
  handler state is in sync with st_table::key_read flag.
  
  All SQL code is supposed to switch KEYREAD optimization
  via st_table::set_keyread().