Update InputReader.cs to safely invoke the event

UOP1_Project/Assets/Scripts/Input/InputReader.cs

 	public void OnMoveSelection(InputAction.CallbackContext context)
 	{
 		if (context.phase == InputActionPhase.Performed)
-			onMoveSelectionEvent();
+			onMoveSelectionEvent?.Invoke();
-			advanceDialogueEvent();
+			advanceDialogueEvent?.Invoke();
 	}