GetTimestamp might delete a field that isn't a timestamp

[kentquirk]

In the loop at the bottom of GetTimestamp(), the function records a name to delete, and then attempts to parse its value. The result of that parse will be a zero Time value if the parse failed (and if so, the loop continues). But if the loop runs without ever finding a valid timestamp, it will still delete the last field that matched one of the names it's searching.

To be fair, if someone has called a field "Timestamp" and this code can't parse it, there are probably bigger problems. But I noticed this while reviewing the code.