Quirk in weight constructor

[afk11]

I was testing this library out and tried rebuilding a Weight object from it's components (weightRange, weight, and format)

It looks like this line: https://github.com/rechner/py-aamva/blob/master/aamva/aamva.py#L1647 is incorrect and causes the weight field to use an approximated value when the exact weight was provided

Weight(5, 200, 'USA') => instead of weight being 200, it was 205 instead

-if weight_range is None:
+if weight is not None:

because when weight is provided, we really don't want the else case triggering, because instead of using the provided weight it calculates weight using the approximation method instead