Fix black-body emission not working when emission color is black

[laurelkeys]

Addresses #2765.

The emission color would incorrectly affect black-body emission behaviour when it was black, as it made compute_edf equal to 0:

appleseed/src/appleseed.shaders/src/appleseed/as_standard_surface.osl

Lines 852 to 860 in bc952ad

	if (compute_edf && in_tonemap_edf)
	{
	edf_color /= luminance(edf_color) + 1.0;
	}
	if (compute_edf && max(edf_color) > 0.0)
	{
	out_outColor += transmittance * opacity *
	edf_color * emission();
	}

Now, in_incandescence_color has no effect when the emission type is "Black-body" (i.e. in_incandescence_type == 1). The "Custom" type behaviour remains unchanged.

[dictoon]

Thanks!