Do not overwrite existing style parts for center images

src/system/papaya_parser.php

@@ -1,21 +1,17 @@
 <?php
 /**
-* Parser for special tags like papaya:media, papaya:link and papaya:popup
-*
-* @copyright 2002-2009 by papaya Software GmbH - All rights reserved.
-* @link http://www.papaya-cms.com/
-* @license http://www.gnu.org/licenses/old-licenses/gpl-2.0.html GNU General Public License, version 2
-*
-* You can redistribute and/or modify this script under the terms of the GNU General Public
-* License (GPL) version 2, provided that the copyright and license notes, including these
-* lines, remain unmodified. papaya is distributed in the hope that it will be useful, but
-* WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
-* FOR A PARTICULAR PURPOSE.
-*
-* @package Papaya
-* @subpackage Core
-* @version $Id: papaya_parser.php 39855 2014-06-05 13:57:21Z weinert $
-*/
+ * papaya CMS
+ *
+ * @copyright 2000-2018 by papayaCMS project - All rights reserved.
+ * @link http://www.papaya-cms.com/
+ * @license http://www.gnu.org/licenses/old-licenses/gpl-2.0.html GNU General Public License, version 2
+ *
+ *  You can redistribute and/or modify this script under the terms of the GNU General Public
+ *  License (GPL) version 2, provided that the copyright and license notes, including these
+ *  lines, remain unmodified. papaya is distributed in the hope that it will be useful, but
+ *  WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+ *  FOR A PARTICULAR PURPOSE.
+ */
 
 /**
 * Parser for special tags like papaya:media, papaya:link and papaya:popup
@@ -602,7 +598,7 @@ function createDynImageTag($params) {
           $style .= ' float: right;';
           break;
         case 'center':
-          $style = ' display: block;  text-align: center;'.
+          $style .= ' display: block;  text-align: center;'.
             ' margin-left: auto;  margin-right: auto;';
           if (isset($style['top']) && $style['top'] > 0) {
             $style .= ' margin-top: '.(int)$borderData['top'].'px;';
@@ -910,7 +906,7 @@ function createImageTag($params, $data) {
         $style .= ' float: right;';
         break;
       case 'center':
-        $style = ' display: block;  text-align: center;'.
+        $style .= ' display: block;  text-align: center;'.
           ' margin-left: auto;  margin-right: auto;';
         if (isset($style['top']) && $style['top'] > 0) {
           $style .= ' margin-top: '.(int)$borderData['top'].'px;';