Fix animated image (GIF) will lose it's kf_imageSource when decoding

Sources/Image.swift

@@ -314,7 +314,7 @@ extension Image {
     
     func kf_decodedImage(scale scale: CGFloat) -> Image? {
         // prevent animated image (GIF) lose it's images
-        if kf_images != nil {
+        if kf_images != nil || kf_imageSource != nil {
             return self
         }