Small bug when selex of oldest age = 0 and N1_model = 1 is used

[GiancarloMCorrea]

Here: https://github.com/timjmiller/wham/blob/master/src/wham_v0.cpp

A selectivity value in line 687 equals zero for the oldest age and for all fleets will cause that FAA_tot(0,n_ages-1) equals zero, so we would have a zero in the denominator in lines 718 and 719. This might be fixed by adding a small constant (1E-03) to the denominator?

[timjmiller]

Thanks! Yes, it should use the value in which_F_age (line 72), similar to the use on line 1230.
I will make this modification to devel branch and reply and close when it is available.

[timjmiller]

This has been fixed on devel branch 4588fc3.