Check for existance of seo_page_title before outputting

lib/template.html

@@ -88,7 +88,7 @@
   <title>{{ seo_title }}</title>
 {% endif %}
 
-{% if seo_title %}
+{% if seo_page_title %}
   <meta property="og:title" content="{{ seo_page_title }}" />
 {% endif %}