update layout

_layouts/default.html

@@ -10,20 +10,22 @@
   </article>
 
   <nav class="pagination">
-    {% assign pages = site.pages | sort: 'order' %}
-    {% for p in pages %}
+    {% assign pages_sorted = site.pages | sort: 'order' %}
+    {% assign current_index = nil %}
+
+    {% for p in pages_sorted %}
       {% if p.url == page.url %}
         {% assign current_index = forloop.index0 %}
       {% endif %}
     {% endfor %}
-    
-    {% if current_index > 0 %}
-      {% assign previous_page = pages[current_index | minus: 1] %}
+
+    {% if current_index and current_index > 0 %}
+      {% assign previous_page = pages_sorted[current_index | minus: 1] %}
       <a href="{{ previous_page.url }}" class="btn btn-primary">&laquo; Previous: {{ previous_page.title }}</a>
     {% endif %}
-    
-    {% if current_index < pages.size %}
-      {% assign next_page = pages[current_index | plus: 1] %}
+
+    {% if current_index and current_index < pages_sorted.size %}
+      {% assign next_page = pages_sorted[current_index | plus: 1] %}
       <a href="{{ next_page.url }}" class="btn btn-primary">Next: {{ next_page.title }} &raquo;</a>
     {% endif %}
   </nav>