fix: prevent exception when imageName is null (#20120)
fix: prevent exception when imageName is null (#20120)

Summary:
When an image source is parsed via `RCTImageFromLocalAssetURL` there seem to be certain situations in which `imageName` is empty from `RCTBundlePathForURL`. Any call to `UIImage imageNamed` with a an empty parameter will throw an exception:

```
CUICatalog: Invalid asset name supplied: '(null)'
```

In my case, the asset URL was pointing to an image in the application sandbox rather than the `NSBundle`. In this case `UIImage imageNamed` was throwing before the call to `NSData dataWithContentsOfURL` below could correctly resolve the image.

This change simply skips the call to `UIImage imageNamed` if no `imageName` value is set.
Pull Request resolved: https://github.com/facebook/react-native/pull/20120

Differential Revision: D14163101

Pulled By: cpojer

fbshipit-source-id: ceec95c02bf21b739962ef5618947a5726ba0473

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