WebP - processing error in Safari

**Describe the bug**
When I try encoding or decoding using the WebP format in Safari, I see a "Processing error".

**To Reproduce**
Steps to reproduce the behavior:
1. Go to https://squoosh.app/
2. Click on "Large photo"
3. On the right, pick "WebP" in dropdown menu to compress
4. See "Processing error" shown on bottom of the page

**Version:**
- OS: macOS Catalina 10.15 (19A602)
- Browser: Safari 13.0.2 (15608.2.30.1.1)

Screenshot:

Start by reproducing the error at squoosh.app in Safari 13.0.2 on macOS Catalina, following the listed Large photo and WebP steps. Trace the WebP encoding and decoding path used by the browser and compare its Safari behavior with other browsers. Done means WebP compression and decoding no longer show “Processing error” in the reported environment.

Written by the indexing model from the issue text.