Don't MVM.updateLayout() until we're ready

MVM.updateLayout was getting called before its htmlInit handler was run. This was due to the statusbar's htmlInit handler running first which triggered a workspace updatelayout which then triggered an MVM updatelayout before MVM was initialized.

Fixes #9114 
@ingorichter 
@JeffryBooher Would a cleaner fix be to ensure WorkspaceManager doesn't start dispatching stuff until after updateReady?  I could imagine other clients of its events getting bit by this too, otherwise.