Make Item_param::val_int and Item_param::val_str follow the used convention...

Make Item_param::val_int and Item_param::val_str follow the used convention and return 0 if null_value==1.

sql/item.cc

@@ -745,6 +745,8 @@ double Item_param::val()
 {
   DBUG_ASSERT(value_is_set == 1);
   int err;
+  if (null_value)
+    return 0.0;
   switch (item_result_type) {
   case STRING_RESULT:
     return (double) my_strntod(str_value.charset(), (char*) str_value.ptr(),
@@ -761,6 +763,8 @@ longlong Item_param::val_int()
 { 
   DBUG_ASSERT(value_is_set == 1);
   int err;
+  if (null_value)
+    return 0;
   switch (item_result_type) {
   case STRING_RESULT:
     return my_strntoll(str_value.charset(),

sql/item.h

@@ -157,6 +157,7 @@ public:
   virtual Item_result result_type () const { return REAL_RESULT; }
   virtual enum_field_types field_type() const;
   virtual enum Type type() const =0;
+  /* valXXX methods must return NULL or 0 or 0.0 if null_value is set. */
   virtual double val()=0;
   virtual longlong val_int()=0;
   virtual String *val_str(String*)=0;