Only add timetable to cache on success

src/main/kotlin/org/mosad/thecitadelofricks/controller/CacheController.kt

@@ -106,7 +106,7 @@ class CacheController {
                         weekNumberYear ?: 0,
                         timetableLink
                     ), timetable ?: TimetableWeek()
-                ).also { timetableList[key] = it }
+                ).also { if (timetable != null) timetableList[key] = it }
             }
         }