fix: Define LastSeen.title_id as Optional[str] (fixes issue #72)

Author: tuxuser

xbox/webapi/api/provider/presence/models.py

@@ -13,7 +13,7 @@ class PresenceLevel(str, Enum):
 
 class LastSeen(CamelCaseModel):
     device_type: str
-    title_id: str
+    title_id: Optional[str]
     title_name: str
     timestamp: str