When `self._sel` is an empty array, `self.blackout()` always returns false. 
When `self._sel` is an empty array, `self.blackout()` always returns false. 

Fixed ChiperSoft/Kalendae#69

mirego/Kalendae,IlanFrumer/Kalendae,IlanFrumer/Kalendae,ChiperSoft/Kalendae,roryf/Kalendae,scientiacloud/Kalendae,ChiperSoft/Kalendae,coreyzev/Kalendae,coreyzev/Kalendae,pfiller/Kalendae,mirego/Kalendae,scientiacloud/Kalendae