This use case occurs when the engine is attempting to do normal/specular compute using lightmap light color but lightgrid light direction:

See #299 about lightcolor restoration, #299 is the deluxemap counterpart of this bug.

The bug may also be related to #320.

We must find a better algorithm or a variant of it for that special use case if we want to support it.

We may want to support it for two reasons:

1. reduce the complexity of the code, avoid intrusive hacky ifdefs everywhere.
2. enable normal mapping on legacy maps.