controllers.users: check flight duration to prevent division by zero
controllers.users: check flight duration to prevent division by zero

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