controllers.flight: check for club=None
controllers.flight: check for club=None

Fixes regression from "controllers.flights: fix club name in json
output".

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