Fix bug: if MIN() or MAX() resulted in a deadlock or a lock wait timeout, MySQL did not return an error, but NULL as the function value


sql/opt_sum.cc:
  Fix bug: if MIN() or MAX() resulted in a deadlock or a lock wait timeout, MySQL did not return an error, but NULL as the function value
sql/sql_select.cc:
  Fix bug: if MIN() or MAX() resulted in a deadlock or a lock wait timeout, MySQL did not return an error, but NULL as the function value