Some series not downloaded on nrk.no

[forthrin]

• I've verified and I assure that I'm running youtube-dl 2018.12.03
• At least skimmed through the README, most notably the FAQ and BUGS sections
• Searched the bugtracker for similar issues including closed ones
• Checked that provided video/audio/playlist URLs (if any) are alive and playable in a browser
• Bug report (encountered problems with youtube-dl)

$ youtube-dl --verbose https://tv.nrk.no/serie/innafor/2018/MDDP12100418/avspiller
[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: [u'--verbose', u'https://tv.nrk.no/serie/innafor/2018/MDDP12100418/avspiller']
[debug] Encodings: locale UTF-8, fs utf-8, out utf8, pref UTF-8
[debug] youtube-dl version 2018.12.03
[debug] Python version 2.7.15 (CPython) - Darwin-16.7.0-x86_64-i386-64bit
[debug] exe versions: ffmpeg 4.0.2, ffprobe 4.0.2, rtmpdump 2.4
[debug] Proxy map: {}
[NRKTVSeries] innafor: Downloading webpage
[download] Downloading playlist: NRK TV – Innafor
[NRKTVSeries] playlist NRK TV – Innafor: Collected 0 video ids (downloading 0 of them)
[download] Finished downloading playlist: NRK TV – Innafor

Happens for this and possibly other -- but not all -- series.