Fixes ScrollView centerContent not work in some cases (#24817)
Fixes ScrollView centerContent not work in some cases (#24817)

Summary:
The bug description can see https://github.com/facebook/react-native/issues/24688, we add `contentView` size check before center the content, because in some cases, the contentView's size not yet be calculated, in those cases, we don't adjust the `contentOffset`.

cc. cpojer .

[iOS] [Fixed] - Fixes ScrollView centerContent not work in some cases
Pull Request resolved: https://github.com/facebook/react-native/pull/24817

Differential Revision: D15322502

Pulled By: sahrens

fbshipit-source-id: e2081f13e9f2e8597a379a9db1607451ea496909

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