Check `splatDetailTex` in mapinfo

Moose says that this entry must be present for splats to work, but at the same time many mappers set it to some fake value which doesn't point to any valid texture. At a glance this sounds like something is misbehaving or is misdesigned. Check what it really does and whether it can be improved (for example maybe the presence of the "real" splat files should just produce the behaviour that mappers currently have to enable by setting `splatDetailTex`).

Start by tracing how mapinfo handles `splatDetailTex` and comparing that behavior with maps containing real splat files. The issue is done when the current requirement and fake-value behavior are confirmed, and a specific improvement is agreed on and validated.

Written by the indexing model from the issue text.