repair some bug on perfectScale

[importos]

Blocks.prototype.perfectScale = function() { if (!this.div) { return; }

var xMin = null, xMax = null;
var yMin = null, yMax = null;

for (var k in this.blocks) {
    var block = this.blocks[k];
    if (xMin == null) {
        xMin = block.x-15
        xMax = block.x+block.width+18;
        yMin = block.y-15
        yMax = block.y+115;
    } else {
        xMin = Math.min(xMin, block.x-15);
        xMax = Math.max(xMax, block.x+block.width+18);
        yMin = Math.min(yMin, block.y-15);
        yMax = Math.max(yMax, block.y+115);
    }
}

[Gregwar]

Hello,

Would you mind opening a pull request instead?

Thanks for contributing