[IMPR] move page checking code from batchLoaded to check_page
[IMPR] move page checking code from batchLoaded to check_page

- decrease nested frow statements
- decrease cyclomatic complexity of batchLoaded method by 10 %

Change-Id: Ic51f2571cbffd47930df5bb50e6f0b8dbecefab6

wikimedia/pywikibot-core,wikimedia/pywikibot-core