Split/Compare function non-functional

[meh9]

The Split/Compare functionality has broken in v8, it no longer creates a second copy of the layer so you can't actually currently compare two different times.

When clicking Compare on the layer as below:

It turns on the splitter, but it does not create the second copy layer to compare with:

When doing the same in a v7 map we get a layer copy:

[nf-s]

This is fixed in #5310

[nf-s]

closed by #5310