Fix original render callback 3rd arg

Author: menno-ll

lib/clarkson-core-gutenberg-block-type.php

@@ -91,7 +91,7 @@ public function clarkson_render_callback( $attributes, $content ) {
 			);
 		}
 		if ( is_callable( $this->original_render_callback ) ) {
-			return (string) call_user_func( $this->original_render_callback, $attributes, $content );
+			return (string) call_user_func( $this->original_render_callback, $attributes, $content, $this );
 		}
 		return $content;
 	}