merge only if page_url is an absolute path

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

@@ -186,8 +186,12 @@ def render("card.json", %{rich_media: rich_media, page_url: page_url}) do
     page_url_data = URI.parse(page_url)
 
     image_url =
+      if %URI{host: nil} = page_url_data do
+        rich_media[:image]
+      else
         URI.merge(page_url_data, URI.parse(rich_media[:image]))
         |> to_string
+      end
 
     site_name = rich_media[:site_name] || page_url_data.host