Fix set default values for range when width entered in percent

When width entered in percent slider set not right default values for range border.

HTML
```html
<p><input type="text" name="slider-options__full-width" id="slider-options__full-width" value="128" data-min="0" data-max="255"/></p>
<p><input type="text" name="slider-range__full-width" id="slider-range__full-width" value="64 192" data-min="0" data-max="255"/></p>
```

JS
```js
$('#slider-options__full-width').slider({
	showValue: true,
	showRange: true,
	minChangeInterval: 500, //fires change event at most every 500ms
	onStart: function(el) {
		console.log('started', el);
	},
	onChange: function(value, el) {
		console.log('progress', value, el);
	},
	onEnd: function(value, el) {
		console.log('end', value, el);
	}
});
$('#slider-range__full-width').slider({
	showValue: true,
	showRange: true,
	onChange: function(valueLeft, valueRight, el) {
		console.log('range progress', valueLeft, valueRight, el);
	}
});
```