Additional fix for bug #21475
item_func.h, item_func.cc:
  Additional fix for bug#16861


sql/item_func.h:
  Additional fix for bug#16861
sql/item_func.cc:
  Additional fix for bug#16861
sql/item_cmpfunc.cc:
  Additional fix for bug #21475
sql/item.cc:
  Additional fix for bug #21475