n-api: avoid crash in napi_escape_scope()

V8 will crash if escape is called twice on the same scope.

Add checks to avoid crashing if napi_escape_scope() is called to try and do this.

Add test that tries to call napi_create_scope() twice.

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• commit message follows [commit guidelines]

Affected core subsystem(s)

n-api