Comment 14 for bug 1789747

I've added some additional sanity checks to the offline caching code to resolve the patron register errors noted above.

Pushed to same branch, but the branch has been rebased to (a busy) master.

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As an aside, I noticed while testing that expire dates are not parsing in Safari, leading to console errors, because it's implementation of Date.parse dislikes time zones like "-0400" -- it prefers "-04:00".