Unexpected behaviour with NR.OBSERVE in multi

`NR.OBSERVE` doesn't reject the wrong number of arguments when in a `MULTI`. Here I'm running `NR.OBSERVE` with no arguments.

```
> MULTI
OK
> NR.OBSERVE
QUEUED
> NR.OBSERVE
QUEUED
> EXEC
1) (error) ERR wrong number of arguments for 'nr.observe' command
2) (error) ERR wrong number of arguments for 'nr.observe' command
```

I would expect that if you run `NR.OBSERVE` you would receive an immediate error and/or trigger an `EXECABORT` when running the `EXEC` command.