redirect_url(): Check the actual URL when https inspecting requests

redirect_url(): Check the actual URL when https inspecting requests

Previously we would only check the path which resulted
in rewrite results being rejected as invalid URLs.

Before:
19:37:29.494 014 Error: pcrs command "s@/test@/@" changed "/test" to "/" (1 hit), but the result doesn't look like a valid URL and will be ignored.

After:
19:40:57.857 002 Redirect: pcrs command s@/test@/@ changed https://www.electrobsd.org/test to https://www.electrobsd.org/ (1 hit).

Reported by withoutname in #1736.