n-api: allow escape of undefined

[mhdawson]

The node-addon-api module was calling escape on undefined
which would fail. Instead of forcing a check in all consumers
of napi_escape_handle accept undefined and simply return
it as it does not need to be escaped.

Refs: nodejs/node-addon-api#233

Checklist

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

[addaleax]

This seems odd … V8 should not make a difference between escaping undefined and other values. In fact, the test code that’s being added here passes on Node 9 for me?

[mhdawson]

@addaleax thanks, I'll take another look. Adding the check in place node-addon-api to avoid the escape resolved the issue in #233 and I figured doing it closer to the source would be better. Maybe it was something in the escape method in node-addon-api as opposed to node_escape_handle.

[mhdawson]

So submitting after putting it together on the plane late night seems to have been a bad idea. I see I used a branch in the node repo instead of my own and that I made it undefined instead of null which was the problem.

Since escaping NULL probably is an error, I'll change the code in node-add-api instead. It requires changing in more places but is probably the right thing to do.