webmention => AP: Create: handle Follower with actor URL instead of object

we don't create these any more, we always fetch and store full actor objects, but we have a few old ones lying around in the prod datastore.

for #33

models.py

@@ -132,7 +132,8 @@ class Follower(StringIdModel):
     Key name is 'USER_DOMAIN FOLLOWER_ID', e.g.:
       'snarfed.org https://mastodon.social/@swentel'.
     """
-    # most recent AP Follow activity (JSON)
+    # most recent AP Follow activity (JSON). must have a composite actor object
+    # with an inbox, publicInbox, or sharedInbox!
     last_follow = ndb.TextProperty()
 
     created = ndb.DateTimeProperty(auto_now_add=True)

webmention.py

@@ -135,14 +135,15 @@ class WebmentionHandler(webapp2.RequestHandler):
 
         if not target:
             # interpret this as a Create or Update, deliver it to followers
-            followers = Follower.query().filter(
+            inboxes = []
+            for follower in Follower.query().filter(
                 Follower.key > Key('Follower', self.source_domain + ' '),
-                Follower.key < Key('Follower', self.source_domain + chr(ord(' ') + 1)))
-            actors = [json.loads(f.last_follow)['actor'] for f in followers
-                      if f.last_follow]
-            inboxes = [a.get('endpoints', {}).get('sharedInbox') or
-                       a.get('publicInbox') or a.get('inbox')
-                       for a in actors]
+                Follower.key < Key('Follower', self.source_domain + chr(ord(' ') + 1))):
+                if follower.last_follow:
+                    actor = json.loads(follower.last_follow).get('actor', {})
+                    inboxes.append(actor.get('endpoints', {}).get('sharedInbox') or
+                                   actor.get('publicInbox')or
+                                   actor.get('inbox'))
             return [(Response.get_or_create(
                         source=self.source_url, target=inbox, direction='out',
                         protocol='activitypub', source_mf2=json.dumps(self.source_mf2)),