package crashes my app when more than 10 cached images widgets are used

## 🐛 Bug Report

when i use more than 10 cached network images my app crashes
this is my code:

```
CachedNetworkImage(
imageUrl: product == null ? productDetails!.imagesUrls[0] : product!.imageUrl,
imageBuilder: (context, imageProvider) {

return Container(
height: 200,
decoration: BoxDecoration(
image: DecorationImage(
image: imageProvider,
fit: BoxFit.cover,
),
),
);

},
progressIndicatorBuilder: (context, url, downloadProgress) {
return Container(
height: 200,
color: Colors.white,
child: Center(
child:CircularProgressIndicator(
value: downloadProgress.progress,
),
),
);
},
errorWidget: (context, url, error) => Icon(Icons.error),
),
```

### Expected behavior

it should not crash :)

### Reproduction steps

### Configuration

**Version:** flutter 2.2.1

**Platform:**
- [ ] :iphone: iOS
- [x] :robot: Android