fix(sticky): NPE in

fixes #7316.

Author: ThomasBurleson

src/components/sticky/sticky.js

@@ -191,7 +191,9 @@ function MdSticky($document, $mdConstant, $$rAF, $mdUtil, $compile) {
       while (current && current !== contentEl[0]) {
         item.top += current.offsetTop;
         item.left += current.offsetLeft;
-        item.right += current.offsetParent.offsetWidth - current.offsetWidth - current.offsetLeft; //Compute offsetRight
+        if ( current.offsetParent ){
+          item.right += current.offsetParent.offsetWidth - current.offsetWidth - current.offsetLeft; //Compute offsetRight
+        }
         current = current.offsetParent;
       }
       item.height = item.element.prop('offsetHeight');