add if for mkdocs versions support

Author: alexey

theme/readthedocs/breadcrumbs.html

@@ -1,13 +1,14 @@
 <div role="navigation" aria-label="breadcrumbs navigation">
   <ul class="wy-breadcrumbs">
     <li><a href="{{ homepage_url }}">Docs v:{{ config.extra.current_version }}</a> &raquo;</li>
-    {% for doc in current_page.ancestors %}
+    {% if current_page %}{% for doc in current_page.ancestors %}
       {% if doc.link %}
         <li><a href="{{ doc.link|e }}">{{ doc.title }}</a> &raquo;</li>
       {% else %}
         <li>{{ doc.title }} &raquo;</li>
       {% endif %}
     {% endfor %}
+    {% endif %}
     {% if current_page %}<li>{{ current_page.title }}</li>{% endif %}
       <li class="wy-breadcrumbs-aside">
         {% if repo_url %}

theme/readthedocs/versions.html

@@ -25,7 +25,7 @@
 
 
 </div>
-    <span><a href="{{ previous_page.url }}" style="color: #fcfcfc;">&laquo; Previous</a></span>
+    {% if previous_page %}<span><a href="{{ previous_page.url }}" style="color: #fcfcfc;">&laquo; Previous</a></span>{% endif %}
     <span style="margin-left: 15px"><a href="{{ next_page.url }}" style="color: #fcfcfc">Next &raquo;</a></span>
 
 </div>