Validation prints `Not found [target]` message for every flag

Version used is 0.9.91.

Running validation with any flags prints a message to console due to how the `positional` args are determined.

E.g. running `--validate src/ --ext foo --attr bar` results in:

```
Not found: /foo
Not found: /bar
```

This is more of a cosmetic issue. I was confused at first when I saw the messages and unsure if my flags were even correctly parsed or not (turns out they are).

Start by tracing the validation path and how positional arguments are determined for --validate, --ext, and --attr. Reproduce the command from the report, then adjust the handling so valid flag values do not produce “Not found” messages while validation and flag parsing continue to work.

Scritto dal modello di indicizzazione a partire dal testo della issue.