Protect CFDD calculation from too high/low plev values

[liammegill]

Type of issue

• bug report

Description

If the input emission inventory has pressure level values that are beyond the contrail grid validity range, the CFDD calculation fails at: plev_ub = cc_plev_vals[plev_idxs]. This is because plev_idxs becomes too large (it adds an extra index beyond the contrail grid validity range). We need to protect the function from these values. Current idea: log a warning and assume all emissions beyond the validity range occur at the extremities (e.g. 1013 hPa at 1000 hPa; 50 hPa at 70 hPa).