returns EOF error when unpack textfile

### What version of Go are you using (`go version`)?

$ go version

go version go1.17.6 darwin/amd64

### What did you do?

unpack textfile with the following code:

```go
tmpFile, err := ioutil.TempFile(os.TempDir(), "")
if err != nil {
log.Fatal("Cannot create temporary file", err)
}

// Remember to clean up the file afterwards
defer os.Remove(tmpFile.Name())

// Example writing to the file
text := []byte("lorem ipsum")
if _, err = tmpFile.Write(text); err != nil {
log.Fatal("Failed to write to temporary file", err)
}
tmpFile.Close()

fileToProcess := tmpFile.Name()
fOpen, err := os.Open(fileToProcess)
if err != nil {
log.Fatal(err)
}
defer fOpen.Close()

_, err = unpackit.Unpack(fOpen, "/tmp/unpackit")
if err != nil {
log.Fatal(err)
}
```

### What did you expect to see?

proper error message, ie: `unsupported file`

### What did you see instead?

`EOF` error