Fix product image import PrestaShop#2

Update my last fix (forget to use "$this->multiple_value_separator" for the separator)

controllers/admin/AdminImportController.php

@@ -1760,7 +1760,7 @@ public function productImport()
 						$product->deleteImages();
 
 				//parse into an array
-				$product->image=explode(',',$product->image);
+				$product->image=explode($this->multiple_value_separator,$product->image);
 
 				if (isset($product->image) && is_array($product->image) && count($product->image))
 				{