`ImageLoader` should remove image for bad `url`

When using a bad image url for a `UImage` :
```swift
UImage(url: $viewModel.map({ $0?.image }), loader: .defaultFade)
```
The existing image is kept, this is a problem when reusing a `UImage`.

Since `ImageLoader` does check the url is 'valid', perhaps it should reset the image before returning?
https://github.com/MihaelIsaev/UIKitPlus/blob/master/Classes/Objects/ImageLoader.swift#L44