f31878bc2c
Fix searches like this:
https://danbooru.donmai.us/artist_urls?search[url_not_regex]=https://www/.artstation/.com/[a-zA-Z0-9-.]
returning a HTTP 500 error with a blank page.
Here the problem is that Postgres raises an error because `[a-zA-Z0-9-.]`
is an invalid character class (it should be `[a-ZA-Z0-9.-]`). This error
happens on the error page itself, when rendering the <link rel="next"> /
<link rel="prev"> links in the <head>, so it causes the error page to fail.