Add workaround for storyboards on priv. instances

An upstream problem with videojs-vtt-thumbnails means that URLs gets
joined incorrectly on any instance where `domain`, `external_port` and
`https_only` aren't set.

This commit adds some logic with the 404 handler to mitigate this
problem. This is however only a workaround.

See:
https://github.com/iv-org/invidious/issues/3117
https://github.com/chrisboustead/videojs-vtt-thumbnails/issues/31

src/invidious/routes/errors.cr

@@ -1,5 +1,10 @@
 module Invidious::Routes::ErrorRoutes
   def self.error_404(env)
+    # Workaround for # 3117
+    if HOST_URL.empty? && env.request.path.starts_with?("/v1/storyboards/sb")
+      return env.redirect "#{env.request.path[15..]}?#{env.params.query}"
+    end
+
     if md = env.request.path.match(/^\/(?<id>([a-zA-Z0-9_-]{11})|(\w+))$/)
       item = md["id"]