Additional escaping in the admin quick edit product view to prevent XSS

Official description: Product backorder stock status.

This vulnerability affects the following application versions:

• WooCommerce 3.3.0
• WooCommerce 3.3.0-rc.1
• WooCommerce 3.3.0-rc.2
• WooCommerce 3.3.1
• WooCommerce 3.3.1-rc.1
• WooCommerce 3.3.2
• WooCommerce 3.3.2-rc.1
• WooCommerce 3.3.3
• WooCommerce 3.3.4
• WooCommerce 3.3.5
• WooCommerce 3.3.6