Off-by-one error in drupal_substr() results in "undefined index" error in includes/unicode.inc line 516

The attached patch fixes an off-by-one error in the drupal_substr() function of the includes/unicode.inc file.

The original code looks like this:

    $strlen = strlen($text);
// ... skipping ...
      $bytes = $istart; $chars = 0;
      while ($bytes < $strlen && $chars < $length) {
        $bytes++;
        $c = ord($text[$bytes]);
        if ($c < 0x80 || $c >= 0xC0) {
          $chars++;
        }
      }

Notice that on the last iteration of the loop, it will try to extract $test[$bytes] where the recently-incremented $bytes value is equal to the length of the $text string. This results in an "undefined index" error, as the element indexes range from [0 .. strlen()-1], not from [1 .. strlen()] as the code would imply.

My corrected version follows:

    $strlen = strlen($text);
// ... skipping ...
      $bytes = $istart+1; $chars = 0;
      while ($bytes < $strlen && $chars < $length) {
        $c = ord($text[$bytes]);
        $bytes++;
        if ($c < 0x80 || $c >= 0xC0) {
          $chars++;
        }
      }

Trivial two-line patch attached, created via "cvs diff" from a current checkout of the DRUPAL-6 branch.