FPD and UX Builder for Flatsome

Hi,

I'm not sure if this is already on a to-do log, but I noticed that the `fpd_products` meta was getting cleared when updating a product by using Flatsome's frontend builder.

I fixed it by adding the following code to `class-admin.php` in `update_custom_meta_fields` function.

if (defined('UX_BUILDER_SAVING') && UX_BUILDER_SAVING)
		    	return $post_id;

I don't feel comfortable editing plugins as they might get overwritten on update, but I couldn't find a way to remove the action in the theme's functions.php since the FPD_Admin class is not accessible via a global variable.

Can you guys take a look at this?

Thanks!