Auto merge of #11264 - KiChjang:fix-anchor-panic, r=metajack
Auto merge of #11264 - KiChjang:fix-anchor-panic, r=metajack

Fix panic from update_href in HTMLAnchorElement

- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy --faster` does not report any errors
- [x] These changes fix #11261 (github issue number if applicable).
- [x] These changes do not require tests because unsure how this would be tested.

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