A wrong order of statements in QUICK_GROUP_MIN_MAX_SELECT::reset
caused a crash when a query with DISTINCT was executed by a loose scan
for an InnoDB table that had been emptied. 


mysql-test/r/innodb_mysql.result:
  Added a test case for bug #26159.
mysql-test/t/innodb_mysql.test:
  Added a test case for bug #26159.
sql/opt_range.cc:
  Fixed bug #26159.
  A wrong order of statements in QUICK_GROUP_MIN_MAX_SELECT::reset
  caused a crash when a query with DISTINCT was executed by a loose scan
  for an InnoDB table that had been emptied. 
  For an empty table quick_prefix_select->reset() was not called at all
  and thus some important initialization steps were missing.