Fix: Initialize sonos timeline cache timestamp (#1524)

Author: nesati

plexapi/sonos.py

@@ -66,6 +66,7 @@ def __init__(self, account, data, timeout=None):
         self._proxyThroughServer = False
         self._showSecrets = CONFIG.get("log.show_secrets", "").lower() == "true"
         self._timeout = timeout or TIMEOUT
+        self._timeline_cache_timestamp = 0
 
     def playMedia(self, media, offset=0, **params):