stream: fix `undefined` in Readable object mode
Fixes this.push(undefined)
.
Fixes: https://github.com/nodejs/node/issues/13753
Checklist
-
make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
tests and/or benchmarks are included -
commit message follows commit guidelines
Affected core subsystem(s)
stream
/cc @nodejs/streams