vertical scroll length should never be 0. This will result in division by 0 errors

Author: nilad

src/js/core/factories/GridRenderContainer.js

@@ -300,7 +300,7 @@ angular.module('ui.grid')
   };
 
   GridRenderContainer.prototype.getVerticalScrollLength = function getVerticalScrollLength() {
-    return this.getCanvasHeight() - this.getViewportHeight() + this.grid.scrollbarHeight;
+    return this.getCanvasHeight() - this.getViewportHeight() + this.grid.scrollbarHeight !== 0 ? this.getCanvasHeight() - this.getViewportHeight() + this.grid.scrollbarHeight : -1;
   };
 
   GridRenderContainer.prototype.getHorizontalScrollLength = function getHorizontalScrollLength() {