Workaround for ERROR RuntimeWarning: overflow encountered in exp

[backeb]

In https://github.com/backeb/dflowfm_ocean_eddy/blob/master/scripts/make_dflowfm_vortex.py find workaround for ERROR RuntimeWarning: overflow encountered in exp

Some solutions:
https://stackoverflow.com/questions/40726490/overflow-error-in-pythons-numpy-exp-function
https://stackoverflow.com/questions/9559346/deal-with-overflow-in-exp-using-numpy