Fix some webp images improperly marked as animated

[Petersmit27]

Depending on the webp file, Element incorrectly detects a webp as animated because the wrong byte is looked at.
If GIF autoplay is disabled, it leads to WEBP files getting the "GIF" banner while they are not actually animated.

Before

After

What was wrong

According to the webp spec referenced in the code, the byte highlighted in the image below is checked, but it should be one in the next row (4 bytes later).

Why the unit test passed before

The Static WEBP test in blobIsAnimated in Image-test.ts passed before this change because the tested file is in the VP8L format, which indeed cannot be animated.

The webp file I have is in the VP8X (extended file) format, which may be animated, but in this case is not.
To make the test fail, you can use it (GitHub doesn't let me directly upload webp files) in place of the current test/unit-tests/images/static-logo.webp.
If needed, I could replace the current static-logo.webp with the one I have for this PR, though maybe you would prefer to have a more serious image for that.

Checklist

• Tests written for new code (and old code if feasible).
• New or updated public/exported symbols have accurate TSDoc documentation.
• Linter and other CI checks pass.
• I have licensed the changes to Element by completing the Contributor License Agreement (CLA)

[t3chguy]

This looks sane, good spot on the byte mistake, but would really want a test. Seriousness of the image matters not, copyright-esque issue however do. Keep in mind the CLA you signed for anything you contribute

[t3chguy]

Well that got a good laugh from me

[Petersmit27]

The added test is pretty minimal, should I add a check that the new file does indeed contain the VP8X bytes? Or should I give some code here for you to verify it? I essentially just added some logs to the blobIsAnimated function

[t3chguy]

@Petersmit27 I trust that you checked it, that's enough

[t3chguy]

Plus in theory coverage will tell us

[t3chguy]

Thanks for this

[t3chguy]

Sorry about the flakes above, they're unrelated to your change and yet to be investigated by the maintainer

[t3chguy]

Going to wait while @florianduros looks into the flakes