[invisible crypto] re-try decrypting messages after we've verified a user (or withdraw verification)

https://github.com/element-hq/matrix-react-sdk/pull/50 enables decrypting in "invisible crypto" mode, and displays an error if you receive an event from a user who was verified, but changed their identity. However, if we re-verify the user (or withdraw verification, when that gets implemented), we don't re-try decrypting, so the error is still shown.