[TC-APP-RELEASE-1C] Mensamodul fängt Wochentage ohne Gerichte nicht ab

Problem

Das Mensamodul geht kaputt, wenn es für den aktuellen Tag keine Gerichte gibt.

NoSuchMethodError: NoSuchMethodError: The method 'weekday' was called on null.
Receiver: null
Tried calling: weekday()
  File "mensa_overview_page.dart", line 75, in _MensaOverviewPageState.build.<fn>
  File "bloc_builder.dart", line 90, in BlocBuilder.build
  File "bloc_builder.dart", line 162, in _BlocBuilderBaseState.build
  File "framework.dart", line 4334, in StatefulElement.build
  File "framework.dart", line 4223, in ComponentElement.performRebuild
  File "framework.dart", line 3947, in Element.rebuild
  File "framework.dart", line 2432, in BuildOwner.buildScope
  File "binding.dart", line 773, in WidgetsBinding.drawFrame
  File "binding.dart", line 283, in RendererBinding._handlePersistentFrameCallback
  File "binding.dart", line 1102, in SchedulerBinding._invokeFrameCallback
  File "binding.dart", line 1041, in SchedulerBinding.handleDrawFrame
  File "binding.dart", line 957, in SchedulerBinding._handleDrawFrame
  File "zone.dart", line 1126, in _rootRun
  File "zone.dart", line 1023, in _CustomZone.run
  File "zone.dart", line 925, in _CustomZone.runGuarded
  File "hooks.dart", line 259, in _invoke
  File "hooks.dart", line 217, in _drawFrame