Cap the discount selector width so long labels do not break the card layout

With MAIN_SHOW_FACNUMBER_IN_DISCOUNT_LIST the option labels get longer
(source invoice ref and date); a plain select sizes itself to its longest
option and could push the left column of the invoice card into the right
one. Cap it at maxwidth500 like other card selectors; without the option
the labels already fit and nothing changes.

Author: Pichinov-Jose

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

@@ -2571,7 +2571,7 @@ public function select_remises($selected, $htmlname, $filter, $socid, $maxvalue
 		dol_syslog(get_class($this) . "::select_remises", LOG_DEBUG);
 		$resql = $this->db->query($sql);
 		if ($resql) {
-			print '<select id="select_' . $htmlname . '" class="flat maxwidth200onsmartphone" name="' . $htmlname . '">';
+			print '<select id="select_' . $htmlname . '" class="flat maxwidth500 maxwidth200onsmartphone" name="' . $htmlname . '">';
 			$num = $this->db->num_rows($resql);
 
 			$qualifiedlines = $num;