Fix corporate information pages error

Some [corporate information pages](https://www.gov.uk/government/organisations/migration-advisory-committee/about)
are erroring because the list of IDs in corporate information groups in the
details hash doesn't match the list of linked corporate information pages
in the links hash.

Even if they do eventually resolve, these two lists will occasionally be
out of sync when they're updated because of the way our publishing system
works. We should defend against this so it doesn't error.

Resolves this [sentry error](https://sentry.io/organizations/govuk/issues/1813208304/?environment=production&project=202226&query=is%3Aunresolved&statsPeriod=14d)

app/presenters/content_item/corporate_information_groups.rb

@@ -61,15 +61,14 @@ def group_title_id(title)
     end
 
     def normalised_group_links(group)
-      group["contents"].map do |group_item|
-        normalised_group_item_link(group_item)
-      end
+      group["contents"].map { |group_item| normalised_group_item_link(group_item) }.compact
     end
 
     def normalised_group_item_link(group_item)
       if group_item.is_a?(String)
         group_item_link = corporate_information_page_links.find { |l| l["content_id"] == group_item }
-        view_context.link_to(group_item_link["title"], group_item_link["base_path"])
+        # it's possible for corporation_information_groups in details and links hashes to be out of sync.
+        view_context.link_to(group_item_link["title"], group_item_link["base_path"]) if group_item_link
       else
         view_context.link_to(group_item["title"], group_item["path"] || group_item["url"])
       end