re-opens the review UI when the postpone operation fails. Before, the
composer would close, even on error, and we would lose the email draft.
Now, the user can decide on how to proceed when postponing fails.
References: https://lists.sr.ht/~rjarry/aerc-devel/patches/28824
Signed-off-by: Koni Marti <koni.marti@gmail.com>