mastodon api: rich media: don't clobber %URI struct with a string

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

@@ -182,11 +182,13 @@ def render("status.json", _) do
   end
 
   def render("card.json", %{rich_media: rich_media, page_url: page_url}) do
+    page_url_data = URI.parse(page_url)
+
     page_url_data =
       if rich_media[:url] != nil do
-        URI.merge(URI.parse(page_url), URI.parse(rich_media[:url]))
+        URI.merge(page_url_data, URI.parse(rich_media[:url]))
       else
-        page_url
+        page_url_data
       end
 
     page_url = page_url_data |> to_string