fetcher: move local object checking into a reusable function

lib/pleroma/object.ex

@@ -255,4 +255,8 @@ defmodule Pleroma.Object do
     |> Object.change(%{data: Map.merge(data || %{}, attrs)})
     |> Repo.update()
   end
+
+  def local?(%Object{data: %{"id" => id}}) do
+    String.starts_with?(id, Pleroma.Web.base_url() <> "/")
+  end
 end

lib/pleroma/object/fetcher.ex

@@ -49,7 +49,7 @@ defmodule Pleroma.Object.Fetcher do
   end
 
   def refetch_object(%Object{data: %{"id" => id}} = object) do
-    with {:local, false} <- {:local, String.starts_with?(id, Pleroma.Web.base_url() <> "/")},
+    with {:local, false} <- {:local, Object.local?(object)},
          {:ok, data} <- fetch_and_contain_remote_object_from_id(id),
          {:ok, object} <- reinject_object(object, data) do
       {:ok, object}