send-email: fix In-Reply-To regression

Fix a regression introduced by

1ca3d6e (send-email: squelch warning due to comparing undefined $_ to "")

where if the user was prompted for an initial In-Reply-To and didn't
provide one, messages would be sent out with an invalid In-Reply-To of
"<>"

Also add test cases for the regression and the fix. A small modification
was needed to allow send-email to take its replies from stdin if the
environment variable GIT_SEND_EMAIL_NOTTY is set.

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

git-send-email.perl

@@ -166,7 +166,9 @@ my $envelope_sender;
 
 my $repo = Git->repository();
 my $term = eval {
-	new Term::ReadLine 'git-send-email';
+	$ENV{"GIT_SEND_EMAIL_NOTTY"}
+		? new Term::ReadLine 'git-send-email', \*STDIN, \*STDOUT
+		: new Term::ReadLine 'git-send-email';
 };
 if ($@) {
 	$term = new FakeTerm "$@: going non-interactive";
@@ -407,8 +409,9 @@ if ($thread && !defined $initial_reply_to && $prompting) {
 	$initial_reply_to = $_;
 }
 if (defined $initial_reply_to) {
-	$initial_reply_to =~ s/^\s*<?/</;
-	$initial_reply_to =~ s/>?\s*$/>/;
+	$initial_reply_to =~ s/^\s*<?//;
+	$initial_reply_to =~ s/>?\s*$//;
+	$initial_reply_to = "<$initial_reply_to>" if $initial_reply_to ne '';
 }
 
 if (!defined $smtp_server) {

t/t9001-send-email.sh

@@ -108,4 +108,25 @@ test_expect_success 'allow long lines with --no-validate' '
 		2>errors
 '
 
+test_expect_success 'Invalid In-Reply-To' '
+	git send-email \
+		--from="Example <nobody@example.com>" \
+		--to=nobody@example.com \
+		--in-reply-to=" " \
+		--smtp-server="$(pwd)/fake.sendmail" \
+		$patches
+		2>errors
+	! grep "^In-Reply-To: < *>" msgtxt
+'
+
+test_expect_success 'Valid In-Reply-To when prompting' '
+	(echo "From Example <from@example.com>"
+	 echo "To Example <to@example.com>"
+	 echo ""
+	) | env GIT_SEND_EMAIL_NOTTY=1 git send-email \
+		--smtp-server="$(pwd)/fake.sendmail" \
+		$patches 2>errors &&
+	! grep "^In-Reply-To: < *>" msgtxt
+'
+
 test_done