Hazard map calculation: set iml = 0 if all poes are zero

[Damiano Monelli]

In the calculation of hazard maps if the probability of exceedance for which the map is computed is larger than the maximum poe in the curves, the minimum iml is taken. Example:

In [9]: poe = 0.4

In [10]: poes = [0.1, 0.2, 0.3]

In [11]: imls = [1, 0.1, 0.01]

In [12]: interp(poe, poes, imls)
Out[12]: 0.01

In this case we should extrapolate to zero instead of returning the minimum iml value.

[Michele Simionato (michele-simionato)]

https://github.com/gem/oq-engine/pull/1413