If assembly is renamed, and existing session is reloaded, can go into infinite loading state

[cmdcolin]

Steps to reproduce

1. Create a small instance of jb2 with an assembly
2. Load an LGV in the browser
3. Rename the assembly in the config file
4. Reload the browser
5. Observe LGV is on an infinite loading...

I think that all assemblyNames are 'statically known' while the "assembly regions" is a lazy loaded/async operation, so I think we can do better than this

Note that in general, this type of thing is not advised for admins, as renaming identifiers including assembly "name" (which is used as identifier) and trackIds, etc can cause lots of issues with reloading sessions, but again, we may be able to do a bit better than infinite loading

[cmdcolin]

this was fixed recently by #4074 with the assembliesNotFound getter on the lgv model