Merge pull request #686 from noesya/fix/unpublished_post_static

Fix static d'un post unpublished

app/views/admin/communication/websites/posts/static.html.erb

 ---
 title: "<%= @about.title %>"
-date: "<%= @about.published_at.iso8601 %>"
+date: "<%= @about.published_at&.iso8601 %>"
 <%= render 'admin/application/static/permalink' %>
 <%= render 'admin/application/static/design', full_width: false, toc_offcanvas: false %>
 <% if @about.pinned %>