add default posts index link to block posts without category

layouts/partials/blocks/templates/posts.html

@@ -18,7 +18,10 @@
             {{ $title_link := false }}
             {{- if $term }}
               {{ $title_link = $term.Permalink }}
-            {{ end -}}
+            {{- else if .all -}}
+              {{ $posts_page := site.GetPage "/posts" }}
+              {{ $title_link = $posts_page.Permalink }}
+            {{- end -}}
 
             {{- if not $title -}}
               {{ partial "blocks/default_title.html" $template }}