prevent php-warnings, closes #2293

Closes #2293

Merge request studip/studip!1517

templates/dates/seminar_export_location.php

 <?
 // condense regular dates by room
-if (is_array($dates['regular']['turnus_data'])) foreach ($dates['regular']['turnus_data'] as $cycle) :
-  if (is_array($cycle['assigned_rooms'])) foreach ($cycle['assigned_rooms'] as $room_id => $count) :
+if (!empty($dates['regular']['turnus_data'])) foreach ($dates['regular']['turnus_data'] as $cycle) :
+  if (!empty($cycle['assigned_rooms'])) foreach ($cycle['assigned_rooms'] as $room_id => $count) :
     $room_object = Room::find($room_id);
     $output[$room_object->name][] = $cycle['tostring_short'] .' ('. $count .'x)';
   endforeach;
 
-  if (is_array($cycle['freetext_rooms'])) foreach ($cycle['freetext_rooms'] as $room => $count) :
+  if (!empty($cycle['freetext_rooms'])) foreach ($cycle['freetext_rooms'] as $room => $count) :
     if ($room) :
       $output['('. $room .')'][] = $cycle['tostring_short']  .' ('. $count .'x)';
     endif;
@@ -16,7 +16,7 @@ endforeach;
 
 
 // condense irregular dates by room
-if (is_array($dates['irregular'])) foreach ($dates['irregular'] as $date) :
+if (!empty($dates['irregular'])) foreach ($dates['irregular'] as $date) :
     if ($date['resource_id']) :
         $output_dates[$date['resource_id']][] = $date;
     elseif ($date['raum']) :
@@ -25,7 +25,7 @@ if (is_array($dates['irregular'])) foreach ($dates['irregular'] as $date) :
 endforeach;
 
 // now shrink the dates for each room/freetext and add them to the output
-if (is_array($output_dates)) foreach ($output_dates as $dates) :
+if (!empty($output_dates)) foreach ($output_dates as $dates) :
     if ($dates[0]['resource_id']) :
         $room_object = Room::find($dates[0]['resource_id']);
         $output[$room_object->name][] = implode(", ", shrink_dates($dates));
@@ -34,10 +34,11 @@ if (is_array($output_dates)) foreach ($output_dates as $dates) :
     endif;
 endforeach;
 
-if (!is_array($output) || count($output) === 0) :
+if (!isset($output) || count($output) === 0) :
   echo _('nicht angegeben');
 elseif (count($output) === 1) :
-  echo array_pop(array_keys($output));
+    $keys = array_keys($output);
+    echo array_pop($keys);
 else :
     $pos = 1;
     foreach ($output as $room => $dates) :