Very wrong colors with ncurses and 30-bit color

Probably related to #25461

VLC versions: git master (82b51438, 2021-03-11) and 3.0.12-1-0-gd147bb5e packaged with Debian

OS: Debian Linux 10.8

Reproducibility: every file tested, every time.

Repro steps:

- Change X11 to use 30-bit (10-bit per color component) color:

$ cat /etc/X11/xorg.conf.d/30-screensetup.conf
Section "Screen"
  Identifier    "Default Screen"
  Monitor        "Configured Monitor"
  Device         "Configured Video Device"
  DefaultDepth    30
EndSection

- Restart computer so that changes take effect
- Play any video file with `nvlc`. The image will not be transparent, like in [#25461](https://code.videolan.org/videolan/vlc/-/issues/25461), but the colors are very wrong

I've attached an example. "correct.jpg" is what it looks like with ffplay. "incorrect.jpg" is what it looks like with nvlc