Added escaping for select query and unserialize data only if it was serialized when using taxanomy

When updating product attributes the old taxonomy slug was not properly escaped. And it’s now only unserializing data if data was serialized.

This vulnerability affects the following application versions:

• WooCommerce 3.2.0
• WooCommerce 3.2.0-rc.1
• WooCommerce 3.2.0-rc.2
• WooCommerce 3.2.1
• WooCommerce 3.2.2
• WooCommerce 3.2.3
• WooCommerce 3.2.4
• WooCommerce 3.2.5
• WooCommerce 3.2.6
• 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
• WooCommerce 3.4.0
• WooCommerce 3.4.0-beta.1
• WooCommerce 3.4.0-rc.1
• WooCommerce 3.4.0-rc.2
• WooCommerce 3.4.1
• WooCommerce 3.4.2
• WooCommerce 3.4.3
• WooCommerce 3.4.4
• WooCommerce 3.4.5