fix: panic when config dir access denied

[oldshensheep]

nali will panic when ConfigDir is not accessible

panic: runtime error: invalid memory address or nil pointer dereference
[signal 0xc0000005 code=0x0 addr=0x18 pc=0x4b8fa2]

goroutine 1 [running]:
github.com/zu1k/nali/internal/constant.prepareDir({0xc000022f40, 0x35})
        github.com/zu1k/nali/internal/constant/path.go:45 +0xe2
github.com/zu1k/nali/internal/constant.init.0()
        github.com/zu1k/nali/internal/constant/path.go:32 +0x1f8

L45 stat is possible nil, we need to check other errs to make sure stat is not nil.
In my case, the err is Access is denied.

nali/internal/constant/path.go

Lines 38 to 48 in 20a0de6

	func prepareDir(dir string) {
	stat, err := os.Stat(dir)
	if err != nil && os.IsNotExist(err) {
	if err := os.MkdirAll(dir, 0755); err != nil {
	log.Fatal("can not create config dir:", dir)
	}
	} else {
	if !stat.IsDir() {
	log.Fatal("path already exists, but not a dir:", dir)
	}
	}

[zu1k]

thanks