Minor fix to 'last changed' field, simplify template and logic

backend/templates/watch-overview.html

@@ -53,7 +53,12 @@
                     {% endif %}
                 </td>
                 <td>{{watch|format_last_checked_time}}</td>
-                <td>{{watch.last_changed|format_timestamp_timeago}}</td>
+                <td>{% if watch.history|length >= 2 and watch.last_changed %}
+                        {{watch.last_changed|format_timestamp_timeago}}
+                    {% else %}
+                        Not yet
+                    {% endif %}
+                </td>
                 <td><a href="/api/checknow?uuid={{ watch.uuid}}{% if request.args.get('tag') %}&tag={{request.args.get('tag')}}{% endif %}" class="pure-button button-small pure-button-primary">Recheck</a>
                     <a href="/edit?uuid={{ watch.uuid}}" class="pure-button button-small pure-button-primary">Edit</a>
                     {% if watch.history|length >= 2 %}