Attempt to fix issue 86

[ocefpaf]

@kwilcox I believe we were relying on a bug and passing an empty y to CubicSpline should return a ValuError but instead we just moved the iteration forward. This PR passes zeroes to ensure we have finite elements to start the iteration.

[kwilcox]

Could we raise a ValueError instead of returning a zeroed out array? That is what the calling function __get_daily_interp_subset expects? Raising a ValueError results in the same outcome.

[ocefpaf]

Could we raise a ValueError instead of returning a zeroed out array? That is what the calling function __get_daily_interp_subset expects? Raising a ValueError results in the same outcome.

That is better. Working on it...

PS: That should probably be in SciPy.