sparse-checkout: correctly set non-cone mode when expected

commit f2e3a218e8 ("sparse-checkout: enable `set` to initialize
sparse-checkout mode", 2021-12-14) made the `set` command able to
initialize sparse-checkout mode, but it also had to function when
sparse-checkout mode was already setup and the user just wanted to
change the sparsity paths.  So, if the user passed --cone or --no-cone,
then we should override the current setting, but if they didn't pass
either, we should use whatever the current cone mode setting is.

Unfortunately, there was a small error in the logic in that it would not
set the in-memory cone mode value (core_sparse_checkout_one) when
--no-cone was specified, but since it did set the config setting on
disk, any subsequent git invocation would correctly get non-cone mode.
As such, the error did not previously matter.  However, a subsequent
commit will add some logic that depends on core_sparse_checkout_cone
being set to the correct mode, so make sure it is set consistently with
the config values we will be writing to disk.

Reviewed-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/sparse-checkout.c

@@ -403,6 +403,7 @@ static int update_modes(int *cone_mode, int *sparse_index)
 		core_sparse_checkout_cone = 1;
 	} else {
 		mode = MODE_ALL_PATTERNS;
+		core_sparse_checkout_cone = 0;
 	}
 	if (record_mode && set_config(mode))
 		return 1;