[FIX] compute the correct offset to adjust view

the jquery method length() compute the height of its element, even if
it is diplay:none.  But in our case, we want the offset to be zero if
there is no visible view_manager_header.  (for example, general settings
in settings menu)

addons/web/static/src/js/search.js

@@ -649,7 +649,7 @@ instance.web.SearchView = instance.web.Widget.extend(/** @lends instance.web.Sea
     // divs).
     adjust_view_top: function () { 
         if (this.$view_manager_header.length) {
-            var height = this.$view_manager_header.height() + 1;
+            var height = this.$view_manager_header[0].offsetHeight + 1;
             this.$view_manager_header.next().css('top', height + 'px');
         }
     },