reftable/stack: unconditionally reload stack after commit

After we have committed an addition to the reftable stack we call `reftable_stack_reload()` to reload the stack and thus reflect the changes that were just added. This function will only conditionally reload the stack in case `stack_uptodate()` tells us that the stack needs reloading. This check is wasteful though because we already know that the stack needs reloading. Call `reftable_stack_reload_maybe_reuse()` instead, which will unconditionally reload the stack. This is merely a conceptual fix, the code in question was not found to cause any problems in practice. Signed-off-by: Patrick Steinhardt <ps@pks.im> Signed-off-by: Junio C Hamano <gitster@pobox.com>