send-email: check for repo before invoking hook

Unless --no-validate is passed, send-email will invoke
$repo->repo_path() in its search for a validate hook regardless of
whether a Git repo is actually present.  Teach send-email to first check
for repo existence.

Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-send-email.perl

@@ -1739,21 +1739,23 @@ sub unique_email_list {
 sub validate_patch {
 	my $fn = shift;
 
-	my $validate_hook = catfile(catdir($repo->repo_path(), 'hooks'),
-				    'sendemail-validate');
-	my $hook_error;
-	if (-x $validate_hook) {
-		my $target = abs_path($fn);
-		# The hook needs a correct cwd and GIT_DIR.
-		my $cwd_save = cwd();
-		chdir($repo->wc_path() or $repo->repo_path())
-			or die("chdir: $!");
-		local $ENV{"GIT_DIR"} = $repo->repo_path();
-		$hook_error = "rejected by sendemail-validate hook"
-			if system($validate_hook, $target);
-		chdir($cwd_save) or die("chdir: $!");
-	}
-	return $hook_error if $hook_error;
+	if ($repo) {
+		my $validate_hook = catfile(catdir($repo->repo_path(), 'hooks'),
+					    'sendemail-validate');
+		my $hook_error;
+		if (-x $validate_hook) {
+			my $target = abs_path($fn);
+			# The hook needs a correct cwd and GIT_DIR.
+			my $cwd_save = cwd();
+			chdir($repo->wc_path() or $repo->repo_path())
+				or die("chdir: $!");
+			local $ENV{"GIT_DIR"} = $repo->repo_path();
+			$hook_error = "rejected by sendemail-validate hook"
+				if system($validate_hook, $target);
+			chdir($cwd_save) or die("chdir: $!");
+		}
+		return $hook_error if $hook_error;
+	}
 
 	open(my $fh, '<', $fn)
 		or die sprintf(__("unable to open %s: %s\n"), $fn, $!);

t/t9001-send-email.sh

@@ -1953,4 +1953,12 @@ test_expect_success $PREREQ 'invoke hook' '
 	)
 '
 
+test_expect_success $PREREQ 'test that send-email works outside a repo' '
+	nongit git send-email \
+		--from="Example <nobody@example.com>" \
+		--to=nobody@example.com \
+		--smtp-server="$(pwd)/fake.sendmail" \
+		"$(pwd)/0001-add-master.patch"
+'
+
 test_done