Fix misleading error message in CashBuyingPowerModel
Fix misleading error message in CashBuyingPowerModel

Fixes #1648

AlexCatarino/Lean,jameschch/Lean,AlexCatarino/Lean,QuantConnect/Lean,QuantConnect/Lean,Jay-Jay-D/LeanSTP,StefanoRaggi/Lean,kaffeebrauer/Lean,QuantConnect/Lean,AnshulYADAV007/Lean,kaffeebrauer/Lean,JKarathiya/Lean,redmeros/Lean,Jay-Jay-D/LeanSTP,jameschch/Lean,JKarathiya/Lean,Jay-Jay-D/LeanSTP,kaffeebrauer/Lean,jameschch/Lean,redmeros/Lean,kaffeebrauer/Lean,AnshulYADAV007/Lean,AnshulYADAV007/Lean,StefanoRaggi/Lean,AlexCatarino/Lean,AnshulYADAV007/Lean,AnshulYADAV007/Lean,kaffeebrauer/Lean,Jay-Jay-D/LeanSTP,AlexCatarino/Lean,QuantConnect/Lean,redmeros/Lean,jameschch/Lean,StefanoRaggi/Lean,JKarathiya/Lean,StefanoRaggi/Lean,StefanoRaggi/Lean,redmeros/Lean,Jay-Jay-D/LeanSTP,jameschch/Lean,JKarathiya/Lean