If loop exit is caused by $i being greater than or equal to $cnt, do try to append the non existent value

class/mime/Rfc822Header.class.php

@@ -179,7 +179,9 @@ class Rfc822Header {
                         }
                         $result .= $value{$i};
                     }
-                    $result .= $value{$i};
+                    if($i < $cnt) {
+                        $result .= $value{$i};
+                    }
                     break;
                 case '(':
                     $depth = 1;
@@ -938,4 +940,4 @@ class Rfc822Header {
     }
 }
 
-?>
+?>