[dev] small mailbox fix

[Vilius Šumskas]

Hello,

this fixes undefined variable error when there are messages flaged 
"Low" in current folder.

-- 
  Best Regards,

  Vilius
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Index: mailbox.php
===================================================================
RCS file: /repository/imp/mailbox.php,v
retrieving revision 2.633
diff -u -r2.633 mailbox.php
--- mailbox.php	20 May 2005 01:54:28 -0000	2.633
+++ mailbox.php	30 May 2005 13:32:30 -0000
@@ -696,7 +696,7 @@
             $msg['bg'] = 'important';
         } elseif ($xprio == 'low') {
             $msg['status'] .= Horde::img('mail_priority_low.png', _("Low Priority"));
-            if ($style[0] == 'b') {
+            if (isset($style[0]) && $style[0] == 'b') {
                 $style = array();
             }
         }