Simplify 'any-check' to only include empty string.

includes/data-stores/class-wc-product-data-store-cpt.php

@@ -1112,7 +1112,7 @@ public function find_matching_product_variation( $product, $match_attributes = a
 
 			// Loop over the variation meta keys and values i.e. what is saved to the products. Note: $attribute_value is empty when 'any' is in use.
 			foreach ( $variation as $attribute_key => $attribute_value ) {
-				$match_any_value = empty( $attribute_value ) && 0.0 !== floatval( $attribute_value );
+				$match_any_value = '' === $attribute_value;
 
 				if ( ! $match_any_value && ! array_key_exists( $attribute_key, $match_attributes ) ) {
 					$match = false; // Requires a selection but no value was provide.