got an unexpected result when a slice contains an invalid string

I got an unexpected result when a slice contains an invalid string

repro:
```go
func TestIssue335(t *testing.T) {
	var v []string
	in := []byte(`["\u","A"]`)
	err := json.Unmarshal(in, &v)
	if err == nil {
		t.Errorf("unexpected success") // unexpected success
	}
	if len(v) != 2 {
		t.Errorf("unexpected result: %q", v) // unexpected result: ["\n"]
	}
}
```