Update VMM.Slider.js

Fix bug when reload introduce less data than previously

Steps to reproduce
* init with 10 dates
* go to 10th date
* reload with 9 dates

source/js/Core/Slider/VMM.Slider.js

@@ -189,7 +189,7 @@ if(typeof VMM != 'undefined' && typeof VMM.Slider == 'undefined') {
 			
 			VMM.Lib.width($slides_items, (slides.length * config.slider.content.width));
 			
-			if (_from_start) {
+			if (_from_start && slides[current_slide] != undefined) {
 				VMM.Lib.css($slider_container, "left", slides[current_slide].leftpos());
 			}