don't try to decrypt a redacted message (fixes vector-im/riot-web#3744)
don't try to decrypt a redacted message (fixes vector-im/riot-web#3744)

set the decrypted data to an empty message

Signed-off-by: Hubert Chathi <394623d3491514d47f1279a4d0ef0068741e3017@uhoreg.ca>

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