Fix problem with horizrailenabled false.

Closes  inuyaksa/jquery.nicescroll#461

jquery.nicescroll.js

@@ -2203,10 +2203,14 @@
         self.scrollratio.x = 0;
         self.cursorwidth = 0;
         self.setScrollLeft(0);
-        self.railh.scrollable = false;
+        if (self.railh) {
+          self.railh.scrollable = false;
+        }
       } else {
-        self.page.maxw -= (self.opt.railpadding.left + self.opt.railpadding.right);  //**
-        self.railh.scrollable = true;
+          self.page.maxw -= (self.opt.railpadding.left + self.opt.railpadding.right);  //**
+          if (self.railh) {
+              self.railh.scrollable = true;
+          }
       }
 
       self.railslocked = (self.locked) || ((self.page.maxh == 0) && (self.page.maxw == 0));