In this case sequencer would allocate empty image buffer which used to not to
have assigned color spaces but it was marked as non-linear float.
Assuming black would always be black in sequencer's color space no additional
transformation for display is needed.
Solved by removing NOLINEAR_FLOAT flag from image buffers and using check
image buffer's float_colorspace for NULL when needed to check whether float
buffer is linear or not.
5badefa8cf