Avoid loading default sidebar if there's a customized one

app/controllers/projects/wikis_controller.rb

@@ -106,9 +106,12 @@ class Projects::WikisController < Projects::ApplicationController
 
     # Call #wiki to make sure the Wiki Repo is initialized
     @project_wiki.wiki
-    @sidebar_wiki_entries = WikiPage.group_by_directory(@project_wiki.pages(limit: 15))
-    # Optional _sidebar.md page
+
     @sidebar_page = @project_wiki.find_page('_sidebar', params[:version_id])
+
+    unless @sidebar_page # Fallback to default sidebar
+      @sidebar_wiki_entries = WikiPage.group_by_directory(@project_wiki.pages(limit: 15))
+    end
   rescue ProjectWiki::CouldNotCreateWikiError
     flash[:notice] = "Could not create Wiki Repository at this time. Please try again later."
     redirect_to project_path(@project)