fixed unstable behaviour of method geodetic.intervals_between

This pr fixes an unstable behavior of the method ``geodetic.intervals_between`` due to floating point errors.

This problem has been found while creating a ``SimpleFaultSurface``. To create the mesh representing the surface, the method ``geodetic.intervals_between`` is called multiple times to create lists of points that are equally spaced between points that are separated by the same distance. Due to floating point errors, the method was calculating different number of intervals between points which were separated by the same distance, and therefore raising an exception when creating a ``SimpleFaultSurface``