'rename layer' should be grayed out when on '(root)'

Summary:

Original bug here: https://bugs.launchpad.net/inkscape/+bug/1321737 (slightly different reproduce now, but still happens)

Steps to reproduce:

(steps 1-2 done in Windows, not sure how other OS's do this)

1. Select an image to open/import into Inkscape in File Explorer (png, jpg).
2. Right click on it and 'Open with' in Inkscape.
3. When the option screen shows up to allow you to either 'embed' or 'link' the image in the file, select either. It doesn't matter which you choose, it happens with both options.
4. Once Inkscape is displaying the image you imported (on a layer called 'Image'), go up to the menu 'Layer' and click 'Delete Layer'.
5. You are now on the '(root)' layer.
6. Layer -> Rename Layer

What happened?

The 'Rename Layer' window shows up allowing you to rename the false '(root)' layer.

What should have happened?

Nothing, as the 'Rename Layer' option should be grayed out and prohibit you renaming '(root)' as it's not a true layer and shouldn't be renamed in the first place. You should get a message at the bottom saying "No Current Layer", just like if you tried to delete it via the "Delete Layer" option.

Sample attachments:

(Use to bypass steps 1 to 4 and go directly to 5) s1418.svg

Version Info:

- Inkscape Version: 1.0 (4035a4fb49, 2020-05-01) x64!
- Operating System: Windows
- Operating System version: Windows 7 x64