When passing a `MessageElement` instead of an init table to
`Message:append_element` in a lua plugin, it would error with "Invalid
message type" suggesting that it calls `elementFromTable`, i.e. acts as
if a `MessageElementInit` table was passed.
```
Reviewed-by: Nerixyz <nerixdev@outlook.de>
Reviewed-by: pajlada <rasmus.karlsson@pajlada.com>
