Register style can be skipped when already registered

src/Spout/Writer/XLSX/Manager/Style/StyleRegistry.php

@@ -119,6 +119,10 @@ class StyleRegistry extends \Box\Spout\Writer\Common\Manager\Style\StyleRegistry
      */
     public function registerStyle(Style $style)
     {
+        if ($style->isRegistered()) {
+            return $style;
+        }
+
         $registeredStyle = parent::registerStyle($style);
         $this->registerFill($registeredStyle);
         $this->registerFormat($registeredStyle);