fs: fix options.end of fs.ReadStream()

Fixes: https://github.com/nodejs/node/issues/18116

options.end of fs.ReadStream does not work when options.start is undefined.

Checklist

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

Affected core subsystem(s)

fs