Recheck next start of tasks from the given one only

		:param task_source: source to check

		:return: None

def __update(self, task_source):
		""" Recheck next start of tasks from the given one only

		:param task_source: source to check

		:return: None
		"""
		next_start = task_source.next_start()
		if next_start is not None:

			if next_start.tzinfo is None or next_start.tzinfo != timezone.utc:
				raise ValueError('Invalid timezone information')

			if self.__next_start is None or next_start < self.__next_start:
				self.__next_start = next_start
				self.__next_sources = [task_source]
			elif next_start == self.__next_start:
				self.__next_sources.append(task_source)