Properly detect if a page has tags or categories

- Arrays are truthy, test on first item instead

_includes/page__taxonomy.html

@@ -5,7 +5,8 @@
   <!-- modified from http://www.codeofclimber.ru/2015/sorting-site-tags-in-jekyll/ -->
 {% endcomment %}
 
-{% if site.tags_archive_filename %}
+{% if page.tags[0] %}
+  {% if site.tags_archive_filename %}
     {% capture page_tags %}{% for tag in page.tags %}{{ tag | downcase }}#{{ tag }}{% unless forloop.last %},{% endunless %}{% endfor %}{% endcapture %}
     {% assign tag_hashes = (page_tags | split: ',' | sort:0) %}
 
@@ -17,9 +18,11 @@
     {% endfor %}
     </span>
     </p>
+  {% endif %}
 {% endif %}
 
-{% if site.categories_archive_filename %}
+{% if page.categories[0] %}
+  {% if site.categories_archive_filename %}
     {% capture page_categories %}{% for category in page.categories %}{{ category | downcase }}#{{ category }}{% unless forloop.last %},{% endunless %}{% endfor %}{% endcapture %}
     {% assign category_hashes = (page_categories | split: ',' | sort:0) %}
 
@@ -31,4 +34,5 @@
     {% endfor %}
     </span>
     </p>
+  {% endif %}
 {% endif %}