API: repository/files GET with file_path with unescaped '.' returns non-json response

Summary

When attempting to get the contents of a repository file from the API, if the file_path parameter ends with '.txt' and the '.' is not properly escaped, the API returns:

{:file_name=>"test.txt", :file_path=>"test.txt", :size=>49, :encoding=>"base64", :content=>"VGhpcyBpcyB0ZXN0IGRhdGEKTW9yZSBkYXRhCmRhdGEKCgpkYXRhIGZvciBldmVyCg==", :ref=>"master", :blob_id=>"b94bf20fbd445f9fd7e0f080d92ddb60bb4786da", :commit_id=>"b43312f78f2480dd8444c9e99c2c810988fcd665", :last_commit_id=>"b43312f78f2480dd8444c9e99c2c810988fcd665"}

This is tested against the currently running version of gitlab on gitlab.com

Similar but not duplicate issue: gitlab-foss#31470 (closed)

Steps to reproduce

1. Create a repository
2. Create a file in that repository called test.txt (or anything ending with .txt)
3. Attempt to GET the file contents using the v4 API as documented here

Example Project

Test Repo

What is the current bug behavior?

API returns invalid data for incorrectly escaped paths

What is the expected correct behavior?

That the API returns valid JSON or no response in every case

Relevant logs and/or screenshots

$ curl --request GET --header 'PRIVATE-TOKEN: <token-here>' 'https://gitlab.com/api/v4/projects/3684663/repository/files/test.txt?ref=master'
{:file_name=>"test.txt", :file_path=>"test.txt", :size=>49, :encoding=>"base64", :content=>"VGhpcyBpcyB0ZXN0IGRhdGEKTW9yZSBkYXRhCmRhdGEKCgpkYXRhIGZvciBldmVyCg==", :ref=>"master", :blob_id=>"b94bf20fbd445f9fd7e0f080d92ddb60bb4786da", :commit_id=>"b43312f78f2480dd8444c9e99c2c810988fcd665", :last_commit_id=>"b43312f78f2480dd8444c9e99c2c810988fcd665"}

Output of checks

This bug happens on GitLab.com

Possible fixes

Unknown