Better error message: "first .: file does not exist"

[guettli]

Is your feature request related to a problem? Please describe.

My migrations' folder was empty, and I was not aware of that. I got that error message:

first .: file does not exist

It took me way too long to find the root cause.

Describe the solution you'd like

I would like to get a better error message, so that I know what is wrong.

Additional context
Add any other context or screenshots about the feature request here.

pgx5

I used that code:

	src := "file://db/migrations"
	m, err := migrate.New(src, dsn)
	if err != nil {
		return err
	}
	defer m.Close()
	if err := m.Up(); err != nil && err != migrate.ErrNoChange {
		return err
	}
	return nil
}

Thank you for go-migrate!