send-email: sanitize author when writing From line

sender is now sanitized, but we didn't sanitize
author when checking whether From: line is needed
in the message body.
As a result git started writing duplicate From lines
when author matched sender and has utf8 characters.

Reported-by: SZEDER Gábor <szeder@ira.uka.de>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Tested-by: SZEDER Gábor <szeder@ira.uka.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
send-email: add test for duplicate utf8 name

Verify that author name is not duplicated if it matches
sender, even if it is in utf8.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>