fix(dialog): backdrop being clipped

This reverts a change from #8349, which caused the backdrop to be clipped if the body was scrolled.

Fixes #8602.

Closes #8611

Author: crisbeto

src/core/util/util.js

@@ -227,18 +227,20 @@ function UtilFactory($document, $timeout, $compile, $rootScope, $$mdAnimate, $in
         var restoreHtmlStyle = htmlNode.style.cssText || '';
         var restoreBodyStyle = body.style.cssText || '';
         var scrollOffset = $mdUtil.scrollTop(body);
+        var clientWidth = body.clientWidth;
 
         if (body.scrollHeight > body.clientHeight + 1) {
           applyStyles(body, {
             position: 'fixed',
             width: '100%',
-            top: -scrollOffset + 'px',
-            overflow: 'hidden'
+            top: -scrollOffset + 'px'
           });
 
           htmlNode.style.overflowY = 'scroll';
         }
 
+        if (body.clientWidth < clientWidth) applyStyles(body, {overflow: 'hidden'});
+
         return function restoreScroll() {
           body.style.cssText = restoreBodyStyle;
           htmlNode.style.cssText = restoreHtmlStyle;