Issue where output file is not created when results present and `-or` flag set

The length of `s.Results` is not guaranteed to have the results stored in it at the time of this check. This is because they may still be sitting in `s.CurrentResults` having not been appended. This means when we use the `-or` argument it will always fail to create a file!

We need to check the length of the result from `append(s.Results, s.CurrentResults...)` as you were doing previously inside each `writeJSON`, `writeEJSON`...

nit: it would be simpler to have one line like:
```
res = append(s.Results, s.CurrentResults...)
```
and use the `res` as an arg to pass to all the output functions.

_Originally posted by @hpy in https://github.com/ffuf/ffuf/pull/444#discussion_r645980300_