BUG: Admin searches in WooCommerce taxonomies return no results

[JakePT]

Describe the bug
When searching within WooCommerce Product Categories or product attributes in the admin with the Terms feature enabled, no results are returned.

With Debug Bar enabled two Elasticsearch queries will be shown. One of them will have no results, but the other one will have the expected results. The queries are exactly the same excerpt two differences. Firstly, the query with no results is sorted with

"sort": [
	{
		"meta.order.long": {
			"order": "asc"
		}
	}
],

And has this additional post_filter:

{
	"bool": {
		"must": [
			{
				"terms": {
					"meta.order.raw": [
						""
					]
				}
			}
		]
	}
}

So the cause has to be something to do with the custom sorting of terms used by WooCommerce.

Steps to Reproduce

1. Install WooCommerce.
2. Import WooCommerce sample data.
3. Go to Products > Categories and search for "Decor". No results are returned.
4. Go to Products > Attributes > color > Configure terms and search for "Gray". No results are returned.
5. Disabled the Terms feature and repeat the searches. Results should be returned as expected.

Expected behavior
Searching terms should return matching terms.