Fixes #5374: webp problem on preload

[CrochetFeve0251]

Description

Fixed a problem where preload didn't handled well webp. For that we changed the is_already_cached method to make it handle webp.

Fixes #5374

Type of change

Please delete options that are not relevant.

• [ ] Enhancement (non-breaking change which improves an existing functionality)

Is the solution different from the one proposed during the grooming?

No.

How Has This Been Tested?

• [ ] Automated Tests

Checklist:

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• [ ] My code follows the style guidelines of this project
• [ ] I have performed a self-review of my own code
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [ ] My changes generate no new warnings
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] New and existing unit tests pass locally with my changes
• [ ] Any dependent changes have been merged and published in downstream modules