copyAssetsVideoIOS not working properly.

```
"react": "16.3.1",
"react-native": "0.55.4",
"react-native-fs": "^2.9.12",
"react-native-gallery-manager": "^1.0.9",
```
Hello there,
I've media picker screen like this,
,
which allow user to select category & media (Images & Video).
So, I'm fetching phone assets from CameraRoll using [react-native-gallery-manager](https://github.com/pentarex/react-native-gallery-manager) library. It's return me images & video URL like, `assets-library://`. this kind of URL can show images properly using [``](https://facebook.github.io/react-native/docs/images), but to load/play video, I need URL like `file://` for [``](https://github.com/react-native-community/react-native-video) & that's why I'm using this package, to fetch video's proper URL.

checkout my code.
```
// GalleryManager Usage
GalleryManager.getAssets({
type: 'all',
limit: 60,
startFrom: this.state.images.length,
}).then(data => this.storeImages(data))

// storeImages Usage
storeImages(data) {

const tempObj = data.assets;
alert('total data get : ' + tempObj.length);
if (tempObj.length > 0) {
const imagesObj = tempObj.filter((tempValue) => tempValue.duration <= 90)
if (Platform.OS === 'ios') {
for (let i = 0; i < imagesObj.length; i++) {
let tempData = imagesObj[i];
if (tempData.type === 'video') {
const res = await RNFS.copyAssetsVideoIOS(
tempData.uri,
`${RNFS.TemporaryDirectoryPath}${tempData.filename}`
)
tempData.uri = "file://" + res;
imagesObj[i] = tempData;
}
}
const imagesData = imagesObj.map(newData => ({
imageLocation: newData.uri,
fileType: newData.mimeType.split('/')[0]
}));
this.setState({
images: [...images, ...imagesData]
});
} else {
const imagesData = imagesObj.map(newData => ({
imageLocation: newData.uri,
fileType: newData.mimeType.split('/')[0]
}));
this.setState({
images: [...images, ...imagesData]
});
}
}

}
```
It's not showing me any output. checkout this images
screenshot is of iPhone Xs max (IOS 12) real device (not of simulator) It's also showing me alert like : `total data get : 60`. however in simulator It's working fine.

if I comment entire `for loop` of my code, It's showing me images properly. checkout following snapshot.

Issue was clear for me that `RNFS.copyAssetsVideoIOS` is not working as expected.
I think this happening because phone contain many 4K quality video & might be It's taking so much time to download video from iCloud as you guys have mentioned [here](https://github.com/itinance/react-native-fs#copyassetsfileiosimageuri-string-destpath-string-width-number-height-number-scale--number--10-compression--number--10-resizemode--string--contain--promisestring). but It's not returning anything forever.

Thank you.
Looking forward to your reply.