Added a case for bug #6365.
item_cmpfunc.cc:
  Fixed bug #6365 : Server crashed when list of values
  in IN predicate contains NULL while the tested field is
  of the character type and not of the default set;
  e.g. when f in 'f IN (NULL,'aa') belongs to binary
  character set, while the default character set is latin1.


sql/item_cmpfunc.cc:
  Fixed bug #6365 : Server crash when list of values
  in IN predicate contains NULL while the tested field is
  of the character type of not of the default set
  e.g. when f in 'f IN (NULL,'aa') belongs to binary
  character set, while the default character set is latin1.
mysql-test/t/func_in.test:
  Added a case for bug #6365.
mysql-test/r/func_in.result:
  Added a case for bug #6365.