plugins.brittv: fix issue with stream url extraction, from 7018fc8 (#1625)
plugins.brittv: fix issue with stream url extraction, from 7018fc8 (#1625)

* plugins.brittv: fix issue with stream url extraction, introduced in 7018fc8

* plugins.brittv: include referer in the http request for the stream url

melmorabity/streamlink,gravyboat/streamlink,back-to/streamlink,bastimeyer/streamlink,javiercantero/streamlink,beardypig/streamlink,gravyboat/streamlink,streamlink/streamlink,javiercantero/streamlink,chhe/streamlink,melmorabity/streamlink,wlerin/streamlink,streamlink/streamlink,chhe/streamlink,back-to/streamlink,bastimeyer/streamlink,beardypig/streamlink,wlerin/streamlink