Closing filter graph workspace causes ngscopeclient to crash when the session is closed

[azonenberg]

Steps to reproduce:

• Open magnitude.scoepsession
• Close filter graph tab
• Close the session

[azonenberg]

also benchmark-vector-magnitude.scopesession

[azonenberg]

Crash is in FilterGraphWorkspace::DoRender in the DockBuilderFinish call. Don't have time to dig into it right now but it seems to be triggered in the first-run path of the newly created session, likely something in dock nodes not getting fully reset?