Fix: add missing closing html tag

Output of extrafields after the selection box for bom (if BOM_SUB_BOM is enabled) was corrupted due to missing closing </select>.

htdocs/core/class/html.form.class.php

@@ -21,6 +21,7 @@
  * Copyright (C) 2018       Nicolas ZABOURI	        <info@inovea-conseil.com>
  * Copyright (C) 2018       Christophe Battarel     <christophe@altairis.fr>
  * Copyright (C) 2018       Josep Lluis Amador      <joseplluis@lliuretic.cat>
+ * Copyright (C) 2023		Joachim Kueter			<git-jk@bloxera.com>
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -2503,6 +2504,7 @@ class Form
 			$error++;
 			dol_print_error($db);
 		}
+		$out .= '</select>';
 		if (empty($nooutput)) {
 			print $out;
 		} else {