Fall back to evaluate_simple in case the search_centers call fails.

[tomaskontrimas]

In case the photospline search_centers call fails (when eventdata is outside photospline boundaries) we can fall back to the slower photospline evaluation (evaluate_simple) which handles this case by returning 0 for the event.

It is relevant for the northern tracks v005p00 and v005p01 datasets.

[tomaskontrimas]

Hi @martwo, could you take a look?

I'm wondering whether it's worth to optimize it by introducing a bit more complex check:
I could set a variable like self.search_centers_failed in the except ValueError: clause, and reset it when initializing the new trial. This would save some time, as following likelihood minimization steps after the first one would not try to call search_centers again.