Undesirably raised black level with ICC profile

Split from #10442

With latest git-master of both libplacebo and mpv, mpv still raises black to R1, G1, B1 with this ICC profile:
notebook.zip

To reproduce, just open this sample video (100% black) with

vo=gpu-next
icc-profile="notebook.icm"

black.zip

Play it in fullscreen, make screenshots and compare with icc-profile="notebook.icm" uncommented: It's 100% black vs. the aforementioned R1, G1, B1. Also, --icc-intent=0 doesn't help. The difference between 100% black and R1, G1, B1 is quite noticeable on my 1050:1 IPS screen when cycling through screenshots in fullscreen.

output.txt

There is no raised black with 3D LUT generated by DisplayCal.

There is also no raised black level when applying full calibration of that ICC profile in Radeon graphics driver via this tool on Windows: https://github.com/dantmnf/AMDColorTweaks
With full calibration via this tool active, I checked black level via colorimeter (i1 Display Plus) & DisplayCal: It's 0.0919 cd/m^2 with and without correction of that ICC profile.

Start by reproducing the report with the supplied notebook.icm and black sample using vo=gpu-next and icc-profile="notebook.icm", then compare fullscreen screenshots with ICC processing disabled. Trace the gpu-next ICC color-management path and determine why 100% black becomes R1, G1, B1; done means black remains unraised while the supplied profile is active.