Fix 500 error on login page if ldap enabled and sign-in disabled

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/views/devise/sessions/new.html.haml

@@ -2,22 +2,22 @@
   .login-heading
     %h3 Sign in
   .login-body
-    - if ldap_enabled? && gitlab_config.signin_enabled
+    - if ldap_enabled?
       %ul.nav.nav-tabs
         - @ldap_servers.each_with_index do |server, i|
-          %li{class: (:active if i==0)}
+          %li{class: (:active if i.zero?)}
             = link_to server['label'], "#tab-#{server['provider_name']}", 'data-toggle' => 'tab'
-        %li
-          = link_to 'Standard', '#tab-signin', 'data-toggle' => 'tab'
+        - if gitlab_config.signin_enabled
+          %li
+            = link_to 'Standard', '#tab-signin', 'data-toggle' => 'tab'
       .tab-content
-        - @ldap_servers.each_with_index do |server,i|
-          %div.tab-pane{id: "tab-#{server['provider_name']}", class: (:active if i==0)}
+        - @ldap_servers.each_with_index do |server, i|
+          %div.tab-pane{id: "tab-#{server['provider_name']}", class: (:active if i.zero?)}
             = render 'devise/sessions/new_ldap', provider: server['provider_name']
-        %div#tab-signin.tab-pane
-          = render 'devise/sessions/new_base'
+        - if gitlab_config.signin_enabled
+          %div#tab-signin.tab-pane
+            = render 'devise/sessions/new_base'
 
-    - elsif ldap_enabled?
-      = render 'devise/sessions/new_ldap', ldap_servers: @ldap_servers
     - elsif gitlab_config.signin_enabled
       = render 'devise/sessions/new_base'
     - else