send-email: ask_default should apply to all emails, not just the first

send-email: ask_default should apply to all emails, not just the first

Commit 6e18251 made the "Send this email?" prompt assume yes if confirm
= "inform" when it was unable to get a valid response. However, the
"yes" assumption only worked correctly for the first email. This commit
fixes the issue and confirms the fix by modifying the existing test for
the prompt to send multiple emails.

Reported by Matthieu Moy <Matthieu.Moy@imag.fr>

Signed-off-by: Jay Soffian <jaysoffian@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>