Errors if the file does not have an alias set

When I first installed this module, my site started throwing a lot of database errors. In short, the file_aliases_preprocess_image_style() function, in line 49 of file_aliases.module tries to query the database for an empty "fid". At least on my Postgres server, this caused a nasty DB error.

Looking at the documentation of drupal_lookup_path, if an alias for that file does not exist, then it returns false. Therefore, I added a check for that false return, in which case it would not try to find an alias. This is my resulted function:

function file_aliases_preprocess_image_style(&$variables) {
  global $base_url;
  $source = drupal_lookup_path('source', str_replace($base_url . base_path(), '', $variables['path']));
  if ($source !== FALSE) {
    $fid = drupal_substr($source, 22);
    if ($uri = db_query("SELECT uri FROM {file_managed} WHERE fid = :fid", array(':fid' => $fid))->fetchField()) {
      $variables['path'] = $uri;
    }
  }
}