MDEV-3873: fixed functions absend in 5.3.

sql/item_func.h

@@ -2053,6 +2053,11 @@ public:
   enum_field_types field_type() const { return last_value->field_type(); }
   bool const_item() const { return 0; }
   void evaluate_sideeffects();
+  void update_uesd_tables()
+  {
+    Item_func_last_value::update_used_tables();
+    maybe_null= last_value->maybe_null;
+  }
 };
 
 

sql/item_strfunc.cc

@@ -341,7 +341,7 @@ String *Item_func_sha2::val_str_ascii(String *str)
 
 void Item_func_sha2::fix_length_and_dec()
 {
-  maybe_null = 1;
+  set_persist_maybe_null(1);
   max_length = 0;
 
 #if defined(HAVE_OPENSSL) && !defined(EMBEDDED_LIBRARY)