Error out earlier on missing mandatory reference

This is the only user of fetch_actor_and_object which previously just
always preteneded to be successful. For all the activity types handled
here, we absolutely need the referenced object to be able to process it
(other than Announce whether or not processing those activity types for
unknown remote objects is desirable in the first place is up for debate)

All other users of the similar fetch_actor already properly check success.

Note, this currently lumps all reolv failure reasons together,
so even e.g. boosts of MRF rejected posts will still exhaust all
retries. The following commit improves on this.

lib/pleroma/web/activity_pub/object_validator.ex

@@ -253,9 +253,12 @@ def fetch_actor(object) do
   end
 
   def fetch_actor_and_object(object) do
-    fetch_actor(object)
-    Object.normalize(object["object"], fetch: true)
-    :ok
+    with {:ok, %User{}} <- fetch_actor(object),
+         %Object{} <- Object.normalize(object["object"], fetch: true) do
+      :ok
+    else
+      _ -> :error
+    end
   end
 
   defp for_each_history_item(

lib/pleroma/web/activity_pub/transmogrifier.ex

@@ -519,10 +519,13 @@ defp handle_incoming_normalised(
 
   defp handle_incoming_normalised(%{"type" => type} = data, _options)
        when type in ~w{Like EmojiReact Announce Add Remove} do
-    with :ok <- ObjectValidator.fetch_actor_and_object(data),
+    with {_, :ok} <- {:link, ObjectValidator.fetch_actor_and_object(data)},
          {:ok, activity, _meta} <- Pipeline.common_pipeline(data, local: false) do
       {:ok, activity}
     else
+      {:link, _} ->
+        {:error, :link_resolve_failed}
+
       e ->
         {:error, e}
     end

lib/pleroma/workers/receiver_worker.ex

@@ -33,6 +33,13 @@ def perform(%Job{args: %{"op" => "incoming_ap_doc", "params" => params}}) do
         Logger.info("Received invalid AP document: (2e) #{inspect(issue)}")
         {:discard, :invalid}
 
+      # failed to resolve a necessary referenced remote AP object;
+      # might be temporary server/network trouble thus reattempt
+      {:error, :link_resolve_failed} = e ->
+        # TODO: lower to debug for PR!
+        Logger.info("Failed to resolve AP link; may retry: #{inspect(params)}")
+        e
+
       {:error, _} = e ->
         Logger.error("Unexpected AP doc error: #{inspect(e)} from #{inspect(params)}")
         e