MastoAPI: Always return an url for statuses.

External url if available, id if not.

lib/pleroma/web/mastodon_api/views/status_view.ex

@@ -80,7 +80,7 @@ def render("status.json", %{activity: %{data: %{"object" => object}} = activity}
     %{
       id: activity.id,
       uri: object["id"],
-      url: object["external_url"],
+      url: object["external_url"] || object["id"],
       account: AccountView.render("account.json", %{user: user}),
       in_reply_to_id: reply_to && reply_to.id,
       in_reply_to_account_id: reply_to_user && reply_to_user.id,

test/web/mastodon_api/status_view_test.exs

@@ -19,7 +19,7 @@ test "a note activity" do
     expected = %{
       id: note.id,
       uri: note.data["object"]["id"],
-      url: note.data["object"]["external_id"],
+      url: note.data["object"]["id"],
       account: AccountView.render("account.json", %{user: user}),
       in_reply_to_id: nil,
       in_reply_to_account_id: nil,