Wrong RegEx to check for local date

[mquadrat]

The regex used in a37_datatype to determine if a given date has a time zone offset is broken., The regex returns true if there is an offset. But the corresponding if interprets the true as "is local date without offset" and adds a "Z" to it.

The if has to be negated. Additionally it might make sense to rename the regex, so it is clear what it does.