don't send start time if offline

app.py

@@ -360,11 +360,12 @@ def heartbeat():
     token = request.args.get('token') or request.cookies.get('token')
     if token in viewers:
         viewers[token]['heartbeat'] = int(time.time())
+    online = is_stream_online()
     return {'viewers': n_viewers(),
-            'online': is_stream_online(),
+            'online': online,
             'current_segment': current_segment(),
             'title': stream_title(),
-            'started': stream_start()}
+            'started': stream_start() if online else None}
 
 
 def _image_to_base64(im):
@@ -552,12 +553,13 @@ def mod():
 @app.route('/stream-info')
 def stream_info():
     start, start_rel = stream_start(absolute=True, relative=True)
+    online = is_stream_online()
     return render_template('stream-info-iframe.html',
                            title=stream_title(),
                            viewer_count=n_viewers(),
-                           stream_start_json=json.dumps(start),
-                           stream_uptime=start_rel,
-                           online=is_stream_online())
+                           stream_start_json=json.dumps(start if online else None),
+                           stream_uptime=start_rel if online else None,
+                           online=online)
 
 @app.route('/teapot')
 def teapot():