Show avatar placeholder in search dropdowns

    
Fixes #18529

app/assets/javascripts/users_select/index.js

@@ -263,7 +263,7 @@ function UsersSelect(currentUser, els, options = {}) {
               const userId = parseInt(input.value, 10);
               const { avatarUrl, avatar_url, name, username, canMerge } = input.dataset;
               return {
-                avatar_url: avatarUrl || avatar_url,
+                avatar_url: avatarUrl || avatar_url || gon.default_avatar_url,
                 id: userId,
                 name,
                 username,