Tasks: Fix php warnings with empty tasks list

apps/tasks/index.php

@@ -34,6 +34,7 @@ foreach( $calendars as $calendar ){
         }
 }
 
+$details = null;
 if( !is_null($id) || count($tasks)){
         if(is_null($id)) $id = $tasks[0]['id'];
         $task = OC_Calendar_Object::find($id);

apps/tasks/templates/part.details.php

@@ -38,5 +38,5 @@ endif; ?>
 	<input type="button" id="tasks_edit" value="<?php echo $l->t('Edit');?>">
 </form>
 <?php else: ?>
-<?php var_dump($_['details']); ?>
+<?php //var_dump($_['details']); ?>
 <?php endif ?>