Fix backup button in logout dialog
Fix backup button in logout dialog

We set the caption appropriately but forgot to actually do the
right thing depending on whether there was a key backup already.

Also fix the loadihng spinner which was never shown.

Fixes https://github.com/vector-im/riot-web/issues/8369

matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk