src: fix missing handlescope bug in inspector

Fix a regression that was introduced in commit 5886e204 ("inspector:
track async stacks when necessary") and that I overlooked during review:
the persistent handle with the callback must be rematerialized *after*
the `v8::HandleScope` is created, not before.

Apparently `test/sequential/test-inspector-async-call-stack.js` has
no test coverage for this scenario and I'm out of good ideas on how
to create a concise and reliable test case.

Fixes: https://github.com/nodejs/node/issues/17496
PR-URL: https://github.com/nodejs/node/pull/17539


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Khaidi Chu <i@2333.moe>
Reviewed-By: Timothy Gu <timothygu99@gmail.com>