fix: don't crash on ctrl-a/-x whith invalid date
fix: don't crash on ctrl-a/-x whith invalid date

sheeprine/khal,pimutils/khal,hobarrera/khal,sithglan/khal,geier/khal,dzoep/khal,sdx23/khal,pdav/khal,sheeprine/khal,sithglan/khal