Fix LQIP generation failing for native WebP/AVIF images

[AsFLY-902]

Problem

LQIP generation fails for natively uploaded WebP and AVIF images. The Utility::drop_webp() function unconditionally strips .webp/.avif extensions, which breaks URLs for native WebP/AVIF files that don't have a double extension (e.g., image.webp vs image.png.webp).

Example:

• image.png.webp → image.png Success (LiteSpeed optimized, has source extension)
• image.webp → image Fails (native WebP, results in 404)

This causes the LQIP service to either:

1. Get a 404 response and add the image to the exclude list
2. Receive an HTML error page instead of image data (Unsupported response content-type text/html) and add the image to the exclude list

Fix

Refactored Utility::drop_webp() to only strip the .webp/.avif suffix when a valid source extension exists underneath (double-extension pattern like .png.webp). Native WebP/AVIF URLs are now returned unchanged.

Changes

• src/utility.cls.php — Updated drop_webp() to use pathinfo() for proper extension detection instead of blind substr() stripping.

[hi-hai]

@timotei-litespeed @AsFLY-902 Please give the latest dev a test to make sure this improved version works as expected.

[timotei-litespeed]

@hi-hai from my tests the change is working as expected.

One thing I want to notice(not error, images are added to preload ): in page VPI metabox there are differences.
V7.8.1:

1
5188350___-1024x1024.jpg

V7.9Beta:

1.webp
5188350___-1024x1024.jpg

Notice the .webp added to first image in 7.9