White screen when performing BT.2390 black point adaptation to BT.1886 from source with black screen

Reproduce:

• BT.2390 tone mapping
• BT.1886 output colorspace
• Blank black frame as input
• HDR peak detection enabled

Most likely what happens here is that peak detection infers the white point as being equal to the black point (0.0), and this somehow hits an edge case in the math formula. Should probably fix this by constraining the peak detection to detect nothing below a certain value.