Update templates to be unchanged when no PyManager is available

Author: zooba

templates/downloads/os_list.html

@@ -43,7 +43,7 @@ <h2>Stable Releases</h2>
                     <li>
                         <a href="{{ r.get_absolute_url }}">{{ r.name }} - {{ r.release_date|date }}</a>
                         {% if os.slug == 'windows' %}
-                            {% if r.is_version_at_least_3_14 %}
+                            {% if latest_pymanager and r.is_version_at_least_3_14 %}
                                 {% if latest_pymanager %}
                                 <p>Download using the <a href="{{ latest_pymanager.get_absolute_url }}">Python install manager</a>.</p>
                                 {% else %}

templates/downloads/supernav.html

@@ -15,6 +15,7 @@ <h4>Download for {{ data.os.name }}</h4>
         <p>
             <a class="button" href="{{ data.python3.url }}">{{ data.python3.release.name }}</a>
         </p>
+        {% if data.os.slug == 'windows' %}<p><strong>Note that Python 3.9+ <em>cannot</em> be used on Windows 7 or earlier.</strong></p>{% endif %}
         {% endif %}
         <p>Not the OS you are looking for? Python can be used on many operating systems and environments. <a href="{% url 'download:download' %}">View the full list of downloads</a>.</p>
     </div>