get ready for the next doodling area

.swift

    func resetDoodleRect() {
        minX = Int(self.frame.width)
        minY = Int(self.frame.height)
        
        maxX = 0
        maxY = 0
        
        lastTouchTimestamp = 0
        
        UIGraphicsBeginImageContextWithOptions(bounds.size, false, 0.0)
        context = UIGraphicsGetCurrentContext()
    }