Cleanly drop state data upon failures and continue processing

[apiology]

Fixes https://github.com/microCOVID/microCOVID/issues/1570

This will drop a state-level locale from the dataset if we encounter an error while processing data within it. #1570 was caused by the upstream JHU data no longer sending data from Pitcairn Islands, which is considered a state-level locale under the UK in the JHU dataset.

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[apiology]

The proximate cause here is that Pitcairn Islands was dropped from JHU's dataset starting 2022-09-14, and update_prevalence.py assumes we will have data for every region it discovers for every day during the 16 days of history we gather:

$ grep Pitcairn 09-13-2022.csv
,,Pitcairn Islands,United Kingdom,2022-09-14 04:20:44,-24.3768,-128.3242,4,0,,,"Pitcairn Islands, United Kingdom",0.0,0.0
$ grep Pitcairn 09-14-2022.csv
$ 

(you can check these at https://raw.githubusercontent.com/CSSEGISandData/COVID-19/master/csse_covid_19_data/csse_covid_19_daily_reports/09-14-2022.csv and so on)

Tested by:

Before fix - running ./update_prevalence.py locally

• verified script failed with error from #1570

After fix - running ./update_prevalence.py locally

• verified that script completed
• verified that UK loads up in site rendered locally
• verified that stale data warning goes away
• verified that Pitcairn Islands is no longer a choice in UK's 'Region' selection