Regression - Local files with a dot in their filenames are not correctly served

Problem/Motivation

It appears that 2.1.3 introduced a regression, specifically #3402972: Fetching does not respect use_imagecache_root when using converted webp image styles
Local files with a dot in their filenames (e.g.: my.file.png) are not correctly served anymore.

Steps to reproduce

Upload a new image with a dot in its name, e.g: my.file.png
When accessing the image style, it is hotlinked to
styles/*/**/my.file?itok=*** instead of
styles/*/**/my.file.png?itok=***

Proposed resolution

Not sure, fix the offending commit.

Digging in the code, the condition here may not be ideal.

Remaining tasks

TODO

User interface changes

TODO

API changes

TODO

Data model changes

TODO