Improve performance of token_replace() if there are no tokens to replace

Currently token_replace() still continues to execute even if it doesn't find any tokens to generate/replace in the text.

We should add a return if token_replace() is empty.

Before:

function token_replace($text, array $data = array(), array $options = array()) {
  $replacements = array();
  foreach (token_scan($text) as $type => $tokens) {
    $replacements += token_generate($type, $tokens, $data, $options);
    if (!empty($options['clear'])) {
      $replacements += array_fill_keys($tokens, '');
    }
  }

  // Optionally alter the list of replacement values.
  if (!empty($options['callback']) && function_exists($options['callback'])) {
    $function = $options['callback'];
    $function($replacements, $data, $options);
  }

  $tokens = array_keys($replacements);
  $values = array_values($replacements);

  return str_replace($tokens, $values, $text);
}

After:

function token_replace($text, array $data = array(), array $options = array()) {
  $scanned_tokens = token_scan($text);
  if (empty($scanned_tokens)) {
    return $text;
  }

  $replacements = array();
  foreach ($scanned_tokens as $type => $tokens) {
    $replacements += token_generate($type, $tokens, $data, $options);
    if (!empty($options['clear'])) {
      $replacements += array_fill_keys($tokens, '');
    }
  }

  // Optionally alter the list of replacement values.
  if (!empty($options['callback']) && function_exists($options['callback'])) {
    $function = $options['callback'];
    $function($replacements, $data, $options);
  }

  $tokens = array_keys($replacements);
  $values = array_values($replacements);

  return str_replace($tokens, $values, $text);
}