Re: FlowWhen using `Board.topics(sort_by='updated')`, after the first batch has been iterated (default is 100 topics), the generator fails with `TypeError`.
```lang=python
from pywikibot.flow import Board
site = pywikibot.Site('test'mediawiki', 'test''mediawiki')
board = Board(site, 'T'Project talk:Sandbox'/Flow test')
topics_list = pageboard.topics(limit=2, sort_by='newest')
for topic in topics_list:
print(topic)
```
returns the expected output:
```
[[test:Topic:T63mvwp0c7chy9c3]]Found 1 mediawiki:mediawiki processes running, including this one.
[[testmediawiki:Topic:T5y39gw54bnw2ice66k4pyiyz5yxuyo]]
[[testmediawiki:Topic:T40a7hu3rdj1w3kv56k61wm97m97zly]]
[[testmediawiki:Topic:T2d0esp9nk0tvt2z3861hfbwvg994dt]]
[[testmediawiki:Topic:T2d0bc2kfgj5z7d247jqwe15hsw3ai0]]
...[[mediawiki:Topic:Sy8491obqj9ak5as]]
```
***[[mediawiki:Topic:T1eljfcxcfozigfo]]
But when `sort_by='updated'` is passed, the following error throws up:[[mediawiki:Topic:T3s5g4btggew2tw3]]
```[[mediawiki:Topic:T3m3vd24vrsb8j1i]]
======================================================================
ERROR: test_topic (tests.flow_thanks_tests.TestFlowThank)
----------------------------------------------------------------------....
Traceback (most recent call last):
File "tests/flow_thanks_tests.py"<console>", line 541, in test_topicin <module>
for topic in topics_list:
File "pywikibot/flow.py", line 140, in topics
data = self.site.load_topiclist(self, **cont_args)
File "pywikibot/site.py", line 1357, in callee
return fn(self, *args, **kwargs)
File "pywikibot/site.py", line 6455, in load_topiclist
offset = pywikibot.Timestamp.fromtimestampformat(offset)
File "pywikibot/__init__.py", line 178, in fromtimestampformat
return cls.strptime(ts, cls.mediawikiTSFormat)
TypeError: must be string, not list
```