Fix negative scroll (e.g. in OS X browsers)

Author: pbock

midnight.jquery.js

@@ -260,6 +260,9 @@
 
         // Check classes are currently active in the header (including the current percentage of each)
         scrollTop = window.pageYOffset || document.body.scrollTop || document.documentElement.scrollTop;
+        // Some browsers (e.g on OS X) allow scrolling past the top/bottom.
+        scrollTop = Math.max(scrollTop, 0);
+        scrollTop = Math.min(scrollTop, $(document).height());
 
         // Get the header's position relative to the document (given that it's fixed)
         var headerHeight = headerInfo.height;