This prevents a potential race condition if control flow ends up in
`ShutdownHTTPServer` before the thread gets to `queue->Run()`,
deleting the work queue while workers are still going to use it.
Meant to fix#12362.
Signed-off-by: Wladimir J. van der Laan <laanwj@gmail.com>
Github-Pull: #12366
Rebased-From: b1c2370dde
Tree-SHA512: 7fbe8e562ba0e1138f95deb42e84cda734bef0d7058349728b3e1602b9f65777c5b1be0f6bd5a7e513ac38487dc82e62fd0a6ee4ed985cbf36c90a7eec18eced