Complete attachment-encryption patch
Complete attachment-encryption patch

https://github.com/matrix-org/matrix-react-sdk/pull/533 originally landed in
the wrong branch, and was reverted by
https://github.com/matrix-org/matrix-react-sdk/pull/546.
https://github.com/matrix-org/matrix-react-sdk/pull/548 attempted to land it on
the develop branch, but omitted a small amount of the patch.

This lands the final part, which got missed out.

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