[myanalysis.py] change in f_chabrier,f_kroup

- if mass_min_global < min(mass_iso) or idem for mass_max_global > max(mass_iso),
  then set to min or maax mass_iso, instead of raise System Exit.
- previously, dN[mass < 0.10] = 0, now dN[mass<0.08] = 0. Either probably
  ok since the isochrones I am using tend to go down to M ~ 0.11 Msun only.