Squizmap #4010 work continues.
These changes are to make the URLs screen work, including the following scenarios:
1. Removing the last web path is no longer banned and will redirect you to a limbo_assetid path with previous treeid,
2. Adding a web path to a limbo_assetid'd asset will redirect it to that new web path,
3. Adding/removing web paths from a page that has no URL due to no web path on a parent, will not redirect at all as none is needed, and will just show "saved".
Files will not redirect for the same reason as point (3) above.