fix: do not try to sub notice period from contract end date if notice period is not set

src/QUI/Memberships/Users/MembershipUser.php

@@ -972,7 +972,11 @@ public function getFrontendViewData()
                 $EndBaseDate->setTime(0, 0, 0);
                 $EndBaseDate->sub(\date_interval_create_from_date_string('1 second'));
 
-                $CancelUntilDate = $EndBaseDate->sub($PeriodOfNoticeInterval);
+                $CancelUntilDate = clone $EndBaseDate;
+
+                if ($PeriodOfNoticeInterval) {
+                    $CancelUntilDate = $EndBaseDate->sub($PeriodOfNoticeInterval);
+                }
             } catch (\Exception $Exception) {
                 QUI\System\Log::writeException($Exception);
             }