Fix: Fix irregular incorrect zero prices

With this change, when the discount price is zero or unset, the proper price is used for the displaying price.

Before this change, `strlen()` was used to check if a discounted price exists, which might not be reliable when 0.00 is passed. (haven't encountred this value yet though)

(possibly) Fixes #4

includes/commons/utilities/Utility.php

@@ -36,9 +36,9 @@ static public function getWooCommerceProductCreatedFromUnitProduct( array $aItem
  $_oWCProduct->set_description( $_oUtil->getElement( $aItem, [ 'feature' ] ) ); // empty string for a default value to avoid `null`. null is not allowed for the `post_content` column
  $_sPriceProper = self::___getPriceProper( $aItem, $_oUtil );
  $_sPriceDiscounted = self::___getPriceDiscounted( $aItem, $_oUtil );
- $_sPriceDisplay = strlen( $_sPriceDiscounted ) ? $_sPriceDiscounted : $_sPriceProper;
+ $_sPriceDisplay = ( 0 < ( double ) $_sPriceDiscounted ) ? $_sPriceDiscounted : $_sPriceProper;
 
- if ( strlen( $_sPriceDiscounted ) ) {
+ if (  0 < ( double ) $_sPriceDiscounted ) {
  $_oWCProduct->set_sale_price( $_sPriceDisplay );
  }
  if ( $_sPriceDisplay ) {