Fixing regression to detect actions with an explicit extension set

[jwoertink]

Purpose

Fixes #2046

Description

A previous PR made an update to auto-detect routes based on extensions used in the request.
If a request came in for /reports.json, it would look for an action with /reports that allowed the JSON mime-type.
If a request came in for /reports.csv, then it would find the action with /reports that allowed the CSV mime-type.

However, if you defined your action as /reports.json explicitly, it would be a 404 🤦‍♂️ This PR
keeps the new auto-detect but also fixes the regression. The downside is that if you rely on the auto-detect now,
it'll technically be 2 route lookups. In the end, correctness is higher priority than performance. We can look at
doing a refactor later that maybe fixes the original issue without breaking compatibility or something.

Checklist

• - An issue already exists detailing the issue/or feature request that this PR fixes
• - All specs are formatted with crystal tool format spec src
• - Inline documentation has been added and/or updated
• - Lucky builds on docker with ./script/setup
• - All builds and specs pass on docker with ./script/test