Improved robustness of file downloads (#225)

lib/pinchflat_web/controllers/media_items/media_item_html/show.html.heex

@@ -32,7 +32,7 @@
               </div>
               <aside class="mt-4 xl:mt-0">
                 <div>Uploaded: <%= @media_item.upload_date %></div>
-                <div>
+                <div :if={URI.parse(@media_item.original_url).scheme =~ "http"}>
                   <.subtle_link href={@media_item.original_url} target="_blank">Open Original</.subtle_link>
                 </div>
                 <div class="mt-4 text-bodydark">