fix: skip fields without env key in onSet

[aymanbagabas]

Options.OnSet gets called on all fields, even the ones that don't have an env key defined. This simply ignore those.

Example: https://go.dev/play/p/U0dET0zgYto

package main

import (
	"fmt"
	"log"

	"github.com/caarlos0/env/v8"
)

type User struct {
	Name     string `env:"NAME"`
	Password string `env:"PASSWORD"`
}

type Config struct {
	User     User   `envPrefix:"USER_"` // this shouldn't be passed to OnSet
	Username string `env:"USERNAME" envDefault:"admin"`
	Password string `env:"PASSWORD"`
}

func main() {
	cfg := &Config{}
	opts := env.Options{
		Prefix: "ENVENV_",
		OnSet: func(tag string, value interface{}, isDefault bool) {
			fmt.Printf("Set %s to %v (default? %v)\n", tag, value, isDefault)
		},
	}

	// Load env vars.
	if err := env.ParseWithOptions(cfg, opts); err != nil {
		log.Fatal(err)
	}

	// Print the loaded data.
	fmt.Printf("%+v\n", cfg)
}

Produces:

Set ENVENV_ to  (default? false)
Set ENVENV_USER_NAME to  (default? false)
Set ENVENV_USER_PASSWORD to  (default? false)
Set ENVENV_USERNAME to admin (default? true)
Set ENVENV_PASSWORD to  (default? false)
&{User:{Name: Password:} Username:admin Password:}

Notice the first line Set ENVENV_ to (default? false) shouldn't really be there

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (3f7d8cf) 100.00% compared to head (1a3ea0b) 100.00%.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #266   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            3         3           
  Lines          426       427    +1     
=========================================
+ Hits           426       427    +1     

Impacted Files	Coverage Δ
env.go	100.00% <100.00%> (ø)

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[caarlos0]

thanks!!