Not all eotf or eotf inverse are well defined for values outside the
intended domain, so just ignore it and clamp it away.
An alternative solution would be to use sign preserving pow here (i.e.
sign(x) * pow(abs(x), p)), however I'm not sure that makes sense or is
defined anywhere. Negative values here are likely a result of colors
being outside the gamut range, so clipping them to 0 is more correct
than mirroring from 0.
This is implemented by a two-subpass rendering scheme; the first
subpass draws (and blends) onto a linear R16G16B16A16_SFLOAT buffer,
while the second subpass performs linear->srgb conversion, writing
onto the actual output buffer.
