Allow animated WEBP's (#1375)

* Don't merge layers when image is animated
* Update src/Drivers/Imagick/Encoders/WebpEncoder.php

---------

Co-authored-by: Oliver Vogel <[email protected]>

Author: phknot

src/Drivers/Imagick/Encoders/WebpEncoder.php

@@ -21,7 +21,10 @@ public function encode(ImageInterface $image): EncodedImage
         $imagick = $image->core()->native();
         $imagick->setImageBackgroundColor(new ImagickPixel('transparent'));
 
-        $imagick = $imagick->mergeImageLayers(Imagick::LAYERMETHOD_MERGE);
+        if (!$image->isAnimated()) {
+            $imagick = $imagick->mergeImageLayers(Imagick::LAYERMETHOD_MERGE);
+        }
+
         $imagick->setFormat($format);
         $imagick->setImageFormat($format);
         $imagick->setCompression($compression);