[FIX] mass_mailing: fixed multiple buttons transcoding issues (outlook hack fix)

Because of outlook hack node was not find next sibling of current element.
Due to this only first button is transcoded into inline css.

addons/web_editor/static/src/js/editor/transcoder.js

@@ -248,6 +248,10 @@ function applyOverDescendants(node, func) {
             func(node);
             applyOverDescendants(node, func);
         }
+        var $node = $(node);
+        if (node.nodeName === 'A' && $node.hasClass('btn') && !$node.children().length && $(node).parents('.o_outlook_hack').length)  {
+            node = $(node).parents('.o_outlook_hack')[0];
+        }
         node = node.nextSibling;
     }
 }