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 
Actually, it looks like it already waits for htmlReady before attaching some resize listeners, so maybe someone else is calling recomputeLayout() before htmlReady -- which might indicate a bug in _that_ code (if it's actually trying to e.g. hide/show panels before htmlReady, that code is probably not working as intended since the also panels won't exist that early).