A handy function to add to Drupal 7 theme to determine if a renderable arrays contain output.

my_theme_has_content.php

/**
 * Checks one or more render arrays for any visible content.
 *
 * @param ...  array One or more renderable arrays.
 *
 * @return bool
 */
function my_theme_has_content() {
  $build = func_get_args();

  // Hash the arguments so we can static cache or tests.
  $key   = md5(json_encode($build));

  // We use some fast static caching to speed multiple calls with the same
  // arguments.
  static $drupal_static_fast;
  if (!isset($drupal_static_fast)) {
    $drupal_static_fast[$key] = &drupal_static(__FUNCTION__, NULL);
  }
  $processed = &$drupal_static_fast[$key];
  if (!isset($processed)) {
    if (($html = render($build))
      // This first check is to remove all tags and look for text...
      && !($processed = (bool) trim(strip_tags($html)))) {
      // ...but It's possible all we have are img tags, so we'll look for at
      // least one image tag and assume this is content.
      $processed = (bool) preg_match('/<(img).+\/>/i', $html);
    }
  }
  
  return $processed;
}