Content filtering ignores vocabularies with only one term

Function : Administer > Content management > Content
Drupal path : admin/content/node

The category filter ignores vocabularies with only one term.
This means that :
1.) The category filter is not displayed unless you define a vocabulary with at least two terms.
2.) If more vocabularies exist, those with only one term do not appear in the category filter selector.

The same happens with the Advanced search function.

The cause of this is in taxonomy.module function taxonomy_form_all()
(comment is mine) :

function taxonomy_form_all($free_tags = 0) {
  $vocabularies = taxonomy_get_vocabularies();
  $options = array();
  foreach ($vocabularies as $vid => $vocabulary) {
    if ($vocabulary->tags && !$free_tags) { continue; }
    $tree = taxonomy_get_tree($vid);
    if ($tree && (count($tree) > 1)) {   /* vocabularies with only one term are skipped */
      $options[$vocabulary->name] = array();
      foreach ($tree as $term) {
        $options[$vocabulary->name][$term->tid] = str_repeat('-', $term->depth) . $term->name;
      }
    }
  }
  return $options;
}

I tested the following modification (see comment):

function taxonomy_form_all($free_tags = 0) {
  $vocabularies = taxonomy_get_vocabularies();
  $options = array();
  foreach ($vocabularies as $vid => $vocabulary) {
    if ($vocabulary->tags && !$free_tags) { continue; }
    $tree = taxonomy_get_tree($vid);
    if ($tree) {   /* Process vocabularies with at least one term. Ignore empty vocabularies. */ 
      $options[$vocabulary->name] = array();
      foreach ($tree as $term) {
        $options[$vocabulary->name][$term->tid] = str_repeat('-', $term->depth) . $term->name;
      }
    }
  }
  return $options;
}

I was not able to find any side-effects, and now all vocabularies with at least one term appear in the content filter selector.

Many thanks for comments/reviews
(patch against HEAD attached)