Fix: "Metro listenting on port undefined"
Fix: "Metro listenting on port undefined"

Summary:
Regression introduced in https://github.com/facebook/react-native/commit/2ad34075f1d048bebb08ef30799ac0d081073150.

Fixes https://github.com/facebook/react-native/issues/18681
Closes https://github.com/facebook/react-native/pull/18722

Differential Revision: D7535684

Pulled By: hramos

fbshipit-source-id: 21bc79091148daba7b668965cd5becaa43117721

facebook/react-native,hoangpham95/react-native,hoangpham95/react-native,janicduplessis/react-native,myntra/react-native,pandiaraj44/react-native,exponent/react-native,facebook/react-native,hammerandchisel/react-native,exponentjs/react-native,facebook/react-native,janicduplessis/react-native,exponentjs/react-native,hammerandchisel/react-native,janicduplessis/react-native,exponentjs/react-native,facebook/react-native,myntra/react-native,javache/react-native,arthuralee/react-native,myntra/react-native,arthuralee/react-native,hammerandchisel/react-native,hoangpham95/react-native,pandiaraj44/react-native,myntra/react-native,hammerandchisel/react-native,exponent/react-native,myntra/react-native,hammerandchisel/react-native,facebook/react-native,exponentjs/react-native,hoangpham95/react-native,hammerandchisel/react-native,exponent/react-native,hoangpham95/react-native,janicduplessis/react-native,exponentjs/react-native,pandiaraj44/react-native,facebook/react-native,pandiaraj44/react-native,exponentjs/react-native,javache/react-native,janicduplessis/react-native,javache/react-native,hammerandchisel/react-native,hammerandchisel/react-native,exponent/react-native,pandiaraj44/react-native,janicduplessis/react-native,arthuralee/react-native,javache/react-native,facebook/react-native,exponent/react-native,javache/react-native,javache/react-native,exponentjs/react-native,myntra/react-native,hoangpham95/react-native,pandiaraj44/react-native,myntra/react-native,javache/react-native,myntra/react-native,javache/react-native,facebook/react-native,pandiaraj44/react-native,javache/react-native,hoangpham95/react-native,exponent/react-native,janicduplessis/react-native,exponent/react-native,exponentjs/react-native,pandiaraj44/react-native,facebook/react-native,hoangpham95/react-native,exponent/react-native,arthuralee/react-native,myntra/react-native,arthuralee/react-native,janicduplessis/react-native