Add null-check for workspace/hotseat.

I assumed that they are non-null, but reportedly it was wrong.
This method can be invoked before the views are fully initialized.
Also hotseat can be null as far as I see setupViews(), therefore
null-check and 'importance stored' flag check should be done
separately.

Bug: 21779078
Change-Id: I3f17226f887c38adf2b1fb7ee2a016e00ffc0eb4