[mythtv] ubuntu ppa master: green screen

[John Pilkington]

I tried 77022ee, which seems to be the first build since the 2019-render 
merge, on my old laptop, again using a window-with-border in kubuntu 
bionic and standard decoding.  All seemed to go well until playback, 
when the sound played but the picture was a uniform green.  I didn't 
find an option set that made it work.  Commits since then are likely to 
have changed this.