Fix show layer inside the layer subgroup

[tmszi]

Reproduce:

1. Add first layer group
2. Add second layer group
3. Move second layer group inside first layer group
4. Add vector map layer inside second layer group
5. Check checkbox on the first layer group

This error message appear on the Console tab:

  File "/usr/local/grass79/gui/wxpython/lmgr/layertree.py",
line 1660, in OnLayerChecked

self.Map.ChangeLayerActive(mapLayer, checked)
  File "/usr/local/grass79/gui/wxpython/core/render.py",
line 1426, in ChangeLayerActive

layer.active = active
AttributeError
:
'NoneType' object has no attribute 'active'

[petrasovaa]

Looks good, thank you, I would like just some small modifications. I would move the if mapLayer: just before self.Map.ChangeLayerActive(mapLayer, checked) since we still probably want to run self.lmgr.WorkspaceChanged(). Also please just add a comment that the condition is for cases when the layer is not map layer but group, it's not obvious.

[tmszi]

All right, I fixed it.

[petrasovaa]

Thank you, merged to 78 as well.