preload based ServiceWorkerFetchTask should not fail if its context is stopped
<rdar://107290643>
Pull request: https://github.com/WebKit/WebKit/pull/12113
Committed 262286@main (e8e52c7a1adc): <https://commits.webkit.org/262286@main> Reviewed commits have been landed. Closing PR #12113 and removing active labels.