forward slash in query string causes Error 404

Grav allows taxonomy terms to contain forward slashes.

For example, the `AC/DC` in:

```yaml
title: Back in Black
taxonomy:
genre: Rock
artist: AC/DC

---
```

However, when processing a search query that contains a forward slash, Grav displays an **Error 404** page. For example:


Here is the URL of that page on the Grav Blog Skeleton demo site:
https://demo.getgrav.org/blog-skeleton/search/query:AC/DC

For comparison, when processing a search query that does *not* contain a forward slash (but still doesn't match any pages), Grav displays a **"found 0 results"** page. For example:


Here is the URL of that page on the Grav Blog Skeleton demo site:
https://demo.getgrav.org/blog-skeleton/search/query:ACDC