fix postprocess_as2() crash on multiply-valued inReplyTo

fixes https://console.cloud.google.com/errors/COTu_PXPjJ2ZWw

common.py

@@ -278,7 +278,7 @@ def postprocess_as2(activity, target=None, key=None):
             if len(in_reply_to) > 1:
                 logging.warning(
                     "AS2 doesn't support multiple inReplyTo URLs! "
-                    'Only using the first: %s' % in_reply_tos[0])
+                    'Only using the first: %s' % in_reply_to[0])
             activity['inReplyTo'] = in_reply_to[0]
 
         # Mastodon evidently requires a Mention tag for replies to generate a

tests/test_common.py

@@ -68,3 +68,11 @@ class CommonTest(testutil.TestCase):
         self.assertIsNone(common.redirect_wrap(None))
         self.assertEqual('', common.redirect_wrap(''))
 
+    def test_postprocess_as2_multiple_in_reply_tos(self):
+        self.assertEqual({
+            'id': 'http://localhost/r/xyz',
+            'inReplyTo': 'foo',
+        }, common.postprocess_as2({
+            'id': 'xyz',
+            'inReplyTo': ['foo', 'bar'],
+        }))