Fix crash

[LinXunFeng]

Fix crash

It will crash when width or height equal zero

let bgImg = UIImage.size(width: 1, height: 0).color(.red).image

let bgImg = UIImage.size(width: 0, height: 1).color(.red).image

[LinXunFeng]

Fix sencond bug

I use two color (fe7338 and fc8e2b), their hashValue are same

so, these codes will be bug

hasher.combine(self.colors)
hasher.combine(self.borderColors)

Resolve: I transform UIColor to HexString before compare hashValue