Fallback generation fails if the file's extension is uppercased

Problem/Motivation

If a file has an uppercase extension ( e.g. : cat-picture.JPG ) the module will not generate a fallback because it fails to match the Drupal\wpf\ImageFactoryInterface::JPG_PATTERN regex.

Steps to reproduce

1. Upload an image with an uppercase extension.
2. Try to open the fallback.

Expected behavior: display the jpg fallback.
Actual behavior: not found error.

Proposed resolution

Simply need to add an /i option to the regex pattern.