Issue #17 : Use $content passed to filter, instead of $post->post_con…

…tent.

Also, wp_unslash() the $content.
Otherwise, the json_decode function will return null.

php/class-post-type.php

@@ -719,7 +719,7 @@ public function filter_out_settings_if_removed_in_metabox( $content ) {
 		}
 
 		$setting_ids_to_unset = $_REQUEST[ $key_for_settings ];
-		$data = json_decode( $post->post_content, true );
+		$data = json_decode( wp_unslash( $content ), true );
 		foreach ( $setting_ids_to_unset as $setting_id ) {
 			unset( $data[ $setting_id ] );
 		}