lib: compensate for duplicate nodes in path

[ArcaTech]

When hitting the back button in a panel, there may be a duplicate node id in the path. This change pops again if the node is still in the path, which fixes having to click the button twice.

I started looking into why this is happening the in the first place, but I haven't figured it out yet. I thought it might help to make a command for the "back" behavior and add this there (and maybe also set workspace.lastOpenedID too?), but I didn't know if that made sense to do before figuring out what the actual problem is first. Anyway, I thought I should get this small change out for review now. Let me know what you think @progrium

[progrium]

I think I've noticed we're inconsistent at properly appending to the path and yeah there may be situations it happens twice. This is good for now.