Fixed misplaced data points on category scale

* Fixed issue, that category scale shows data points misplaced. See #4060
* Cleaned code
* Fixed Irregular whitespace
* Fixed error in case value is undefined
* Verified that no error is thrown in case value === null

Author: martinzuern

src/scales/scale.category.js

@@ -66,8 +66,15 @@ module.exports = function(Chart) {
 			// 1 is added because we need the length but we have the indexes
 			var offsetAmt = Math.max((me.maxIndex + 1 - me.minIndex - ((me.options.gridLines.offsetGridLines) ? 0 : 1)), 1);
 
-			if (value !== undefined && isNaN(index)) {
+			// If value is a data object, then index is the index in the data array,
+			// not the index of the scale. We need to change that.
+			var valueCategory;
+			if (value !== undefined && value !== null) {
+				valueCategory = me.isHorizontal() ? value.x : value.y;
+			}
+			if (valueCategory !== undefined || (value !== undefined && isNaN(index))) {
 				var labels = me.getLabels();
+				value = valueCategory || value;
 				var idx = labels.indexOf(value);
 				index = idx !== -1 ? idx : index;
 			}