streamer: use direct object for filter checks when there is no valid child object in an activity

We call Object.normalize/1 to get the child object for situations like Announce.
However, the check is flawed and immediately fails if Object.normalize/1 fails.
Instead, we should use the activity itself in those cases to allow activities which
never have a child object to pass through the filter.

Closes #1291

lib/pleroma/web/streamer/worker.ex

@@ -136,7 +136,7 @@ defmodule Pleroma.Web.Streamer.Worker do
     recipients = MapSet.new(item.recipients)
     domain_blocks = Pleroma.Web.ActivityPub.MRF.subdomains_regex(user.info.domain_blocks)
 
-    with parent when not is_nil(parent) <- Object.normalize(item),
+    with parent <- Object.normalize(item) || item,
          true <- Enum.all?([blocks, mutes, reblog_mutes], &(item.actor not in &1)),
          true <- Enum.all?([blocks, mutes], &(parent.data["actor"] not in &1)),
          true <- MapSet.disjoint?(recipients, recipient_blocks),