Infinite loop with some documents

```xml
<?xml version="1.0" encoding="utf-8"?>
<feed xmlns="http://www.w3.org/2005/Atom">
  <title type="html">
      Less: &lt;em> &amp;lt; &lt;/em>
  </title>
</feed>
```
or

```xml
<a><b>></b></a>
```

```go
	var a struct {
		XMLName xml.Name
	}

	err := xml.Unmarshal([]byte(s), &a)
	fmt.Println(err)
```


It works with `encoding/xml`.