Allow undefined Response status
Allow undefined Response status

This allows the Response constructor to accept a status code that's
explicitly set to undefined. Native fetch implementations in Chrome and
Firefox behave this way.

The following now works, but would previously throw an error:

    new Response('', { status: undefined })

JhansiYarnagula/dummy2,github/fetch,JhansiYarnagula/dummy2,aleclarson/fetch,JhansiYarnagula/dummy2