improve tab component index

Author: lovasoa

examples/official-site/component.sql

@@ -1,7 +1,7 @@
 -- ensure that the component exists and do not render this page if it does not
 select 'redirect' as component,
-    'component_not_found.sql?component=' || sqlpage.url_encode($component) as link
-where $component is not null and not exists (select 1 from component where name = $component);
+    'component_not_found.sql' || coalesce('?component=' || sqlpage.url_encode($component), '') as link
+where not exists (select 1 from component where name = $component);
 
 -- This line, at the top of the page, tells web browsers to keep the page locally in cache once they have it.
 select 'http_header' as component, 'public, max-age=600, stale-while-revalidate=3600, stale-if-error=86400' as "Cache-Control";

examples/official-site/component_not_found.sql

@@ -1,3 +1,5 @@
+select 'http_header' as component, 'noindex' as "X-Robots-Tag";
+
 select 'dynamic' as component, properties FROM example WHERE component = 'shell' LIMIT 1;
 
 select 

examples/official-site/sqlpage/migrations/13_tab.sql

@@ -88,9 +88,9 @@ View the [dynamic tabs example](examples/tabs.sql).
         JSON(
             '[
             { "component": "tab" },
-            { "title": "My First tab", "active": true },
-            { "title": "This is tab two" },
-            { "title": "Third tab is crazy" }
+            { "title": "This tab does not exist", "active": true },
+            { "title": "I am not a true tab" },
+            { "title": "Do not click here" }
         ]'
         )
     ),