fix multiple issues in index-pack

Since commit 9441b61dc5, two issues affected correct behavior of
index-pack:

 1) The real_type of a delta object is the 'real_type' of its base, not
    the 'type' which can be a "delta type".  Consequence of this is a
    corrupted pack index file which only needs to be recreated with a
    good index-pack command ('git verify-pack' will flag those).

 2) The code sequence:

        result->data = patch_delta(get_base_data(base), base->obj->size,
                                   delta_data, delta_size, &result->size);

    has two issues of its own since base->obj->size should instead be
    base->size as we want the size of the actual object data and not
    the size of the delta object it is represented by.  Except that
    simply replacing base->obj->size with base->size won't make the
    code more correct as the C language doesn't enforce a particular
    ordering for the evaluation of needed arguments for a function call,
    hence base->size could be pushed on the stack before get_base_data()
    which initializes base->size is called.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Tested-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

index-pack.c

@@ -514,15 +514,14 @@ static void *get_base_data(struct base_data *c)
 static void resolve_delta(struct object_entry *delta_obj,
 			  struct base_data *base, struct base_data *result)
 {
-	void *delta_data;
-	unsigned long delta_size;
+	void *base_data, *delta_data;
 
-	delta_obj->real_type = base->obj->type;
+	delta_obj->real_type = base->obj->real_type;
 	delta_data = get_data_from_pack(delta_obj);
-	delta_size = delta_obj->size;
+	base_data = get_base_data(base);
 	result->obj = delta_obj;
-	result->data = patch_delta(get_base_data(base), base->obj->size,
-				   delta_data, delta_size, &result->size);
+	result->data = patch_delta(base_data, base->size,
+				   delta_data, delta_obj->size, &result->size);
 	free(delta_data);
 	if (!result->data)
 		bad_object(delta_obj->idx.offset, "failed to apply delta");