Plugin Directory Search errors 502 on Firefox

[Ipstenu]

On firefox, the first time you run a search for anything (on either old or new) you get a 502 nginx error and the URL doesn't redirect:

​https://wordpress.org/plugins-wp/?s=asdasase

If you hit refresh, it's fine.

This only happens on Firefox. I think it's an issue with the nguni redirect but I'm not sure how.

[tellyworth]

In 4457:

Plugin directory: don't trigger an ElasticSearch query if the search will redirect to a pretty URL.

This eliminates double queries and appears to fix the 502 error in Firefox.

Fixes #2275