Resolve "Keine Veranstaltungstermin im Kalender", fixes #2218

Closes #2218

Merge request studip/studip!1450

lib/classes/calendar/SingleCalendar.php

@@ -1234,13 +1234,14 @@ class SingleCalendar
         $properties = $event->getProperties();
         if (is_array($restrictions)) {
             foreach ($restrictions as $property_name => $restriction) {
-                if (is_array($restriction) && isset($properties[mb_strtoupper($property_name)])) {
-                    return in_array($properties[mb_strtoupper($property_name)], $restriction);
-                } else if ($restriction != '') {
-                    return isset($properties[mb_strtoupper($property_name)]) && $properties[mb_strtoupper($property_name)] === $restriction;
+                if (isset($properties[mb_strtoupper($property_name)])) {
+                    if (is_array($restriction)) {
+                        return in_array($properties[mb_strtoupper($property_name)], $restriction);
+                    } else if ($restriction != '') {
+                        return $properties[mb_strtoupper($property_name)] == $restriction;
+                    }
                 }
             }
-            return true;
         }
         return true;
     }