fix typo in variable name

Reported by Gabriele Vivinetto (gabrielev@SF),
https://sourceforge.net/tracker/?func=detail&aid=3266862&group_id=191583&atid=937964


git-svn-id: https://svn.code.sf.net/p/postfixadmin/code/trunk@1024 a1433add-5e2c-0410-b055-b7f2511e0802

ADDITIONS/squirrelmail-plugin/functions.inc.php

@@ -92,7 +92,7 @@ $optmode = 'display';
 // Call: check_email (string email)
 //
 function check_email ($email) {
-    $return = filter_var('validate_email', $emai);
+    $return = filter_var('validate_email', $email);
     if($return === false) {
         return false;
     }