AbstractCalibratedSpace: fix recursion bug

The default CalibratedSpace#averageScale(int) implementation was
*supposed* to call axis(int).averageScale(0, 1), since in the case of
CalibratedSpaces which may not be Intervals, we do not know of any
better bounds to use.

Somehow, I mangled it and the problem was not caught until now. So this
change also adds a unit test to ensure the problem does not recur.