Fix TypeError when no User Agent is provided.
Fix TypeError when no User Agent is provided.

florenceyeun/reddit-plugin-liveupdate,madbook/reddit-plugin-liveupdate,florenceyeun/reddit-plugin-liveupdate,madbook/reddit-plugin-liveupdate,florenceyeun/reddit-plugin-liveupdate,sim642/reddit-plugin-liveupdate,sim642/reddit-plugin-liveupdate,madbook/reddit-plugin-liveupdate,sim642/reddit-plugin-liveupdate