prevent php-warnings, closes #2248

Closes #2248

Merge request studip/studip!1481

app/views/course/details/index.php

@@ -363,7 +363,7 @@
     </article>
 <? endif ?>
 
-<? if ($study_areas && count($study_areas) > 0) : ?>
+<? if (!empty($study_areas)) : ?>
     <article class="studip">
         <header>
             <h1><?= _('Studienbereiche') ?></h1>

app/views/study_area/tree.php

@@ -6,6 +6,7 @@
  * @var array $dont_open
  * @var string $compulsory
  */
+$layer = 0;
 ?>
 <li>
 <? if ($node->id !== 'root' && $node->required_children): ?>

templates/dates/seminar_html_location.php

@@ -11,7 +11,7 @@ if (is_array($dates['regular']['turnus_data'])) foreach ($dates['regular']['turn
     if ($cycle['desc'])
         $cycle_output .= ', <i>' . htmlReady($cycle['desc']) . '</i>';
 
-    if ($show_room) :
+    if (!empty($show_room)) :
         $cycle_output .= $this->render_partial('dates/_seminar_rooms', ['assigned' => $cycle['assigned_rooms'],
                                                                         'freetext' => $cycle['freetext_rooms'],
                                                                         'link'     => $link