Don't setState after unmounting a component
Don't setState after unmounting a component

Fix a warning which happens if a LinkPreviewWidget is unmounted before the
preview request completes.

Also add missing .done to promise chain

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