Hotfix: polygon table coverage

[hannahker]

Addressing #23 and #19.

The polygon table on prod is missing all pcodes for NGA and TCD. This was fixed when #16 was merged. However these changes and the integration of Floodscan (see #25) caused issues where 'PRI', 'FJI', 'UZB', 'KIR', and 'BRA' were dropped from the polygon table. This is because of an error due to the fact that these iso3s all slightly overlap with the edges of the floodscan raster so that they aren't caught with this condition. This results in the iso3 being dropped for all datasets.

This PR fixes the issue with a more complete check against the coverage for a given dataset.

This diff overrepresents the changes all because of a change in indentation. Basically I've just added the following flag:

coverage = check_coverage(row, dataset)
if coverage:
     # everything the same as before...
else:
     logger.info(f"Skipping calculation for {dataset} for {iso3}")

[hannahker]

FYI @zackarno once this is merged I'll update the polygon table and this should address all missing pcode issues.

[isatotun]

I think I understand where this is going. LGTM