Added a comment about Announces of non-Notes.

activitypub.c

@@ -1497,6 +1497,11 @@ int process_input_message(snac *snac, xs_dict *msg, xs_dict *req)
 
         timeline_request(snac, &object, &wrk);
 
+        /* Note: implementations like lemmy send announces about objects
+           that are not of the 'Note' type; these objects are not stored,
+           so the following object_get() will fail even if the object
+           was correctly requested */
+
         if (valid_status(object_get(object, &a_msg))) {
             char *who = xs_dict_get(a_msg, "attributedTo");