Gracefully handling invalid input for duration field

[jareware]

It seems that quite a few people have added some extra characters to the "number of days of symptoms" field. Like "7p" or "7 " instead of just "7". Our draconian validation rules have rejected such input, and our privacy-oriented design means there's no logs of those rejected payloads. 🤦‍♂️

For instance, during the 27th (big public launch) we got a total of 26779 responses, and total of 264 such failures. Many of these also seem to be the same person trying a few times to submit, only to get the "couldn't submit, please try again" error. A cursory glance over the logs suggests something like 10 retries on average, before the participant either gets it right, or gives up. So with those numbers, for the 27th, we've lost ~0.1% of potential responses due to this overly-strict validation. 😿

Some folks apparently also put in e.g. "-", or "?" or some such. These should be automatically converted to empty, while "7 " should obviously be treated the same as "7".

[jareware]