iconv rather than mbstring for convert encoding

Author: Mark Baker

Classes/PHPExcel/Shared/String.php

@@ -491,14 +491,14 @@ public static function UTF8toBIFF8UnicodeLong($value)
  */
 public static function ConvertEncoding($value, $to, $from)
 {
-if (self::getIsMbstringEnabled()) {
-return mb_convert_encoding($value, $to, $from);
-}
-
 if (self::getIsIconvEnabled()) {
 return iconv($from, $to, $value);
 }
 
+if (self::getIsMbstringEnabled()) {
+return mb_convert_encoding($value, $to, $from);
+}
+
 if($from == 'UTF-16LE'){
 return self::utf16_decode($value, false);
 }else if($from == 'UTF-16BE'){