model/flight: Fixed None checks
model/flight: Fixed None checks

This had the potential to throw TypeErrors

Turbo87/skylines,RBE-Avionik/skylines,Turbo87/skylines,shadowoneau/skylines,Harry-R/skylines,RBE-Avionik/skylines,kerel-fs/skylines,Harry-R/skylines,RBE-Avionik/skylines,TobiasLohner/SkyLines,snip/skylines,shadowoneau/skylines,RBE-Avionik/skylines,skylines-project/skylines,dkm/skylines,Turbo87/skylines,Harry-R/skylines,Harry-R/skylines,skylines-project/skylines,skylines-project/skylines,dkm/skylines,kerel-fs/skylines,snip/skylines,Turbo87/skylines,shadowoneau/skylines,dkm/skylines,kerel-fs/skylines,TobiasLohner/SkyLines,TobiasLohner/SkyLines,dkm/skylines,skylines-project/skylines,shadowoneau/skylines,snip/skylines