only clobber displayname & avatarurl from presence if set. fixes https://github.com/vector-im/vector-web/issues/1039. again.
only clobber displayname & avatarurl from presence if set. fixes https://github.com/vector-im/vector-web/issues/1039. again.

krombel/matrix-js-sdk,matrix-org/matrix-js-sdk,williamboman/matrix-js-sdk,krombel/matrix-js-sdk,matrix-org/matrix-js-sdk,williamboman/matrix-js-sdk,krombel/matrix-js-sdk,matrix-org/matrix-js-sdk,williamboman/matrix-js-sdk,matrix-org/matrix-js-sdk