Properly zero out data. Closes #53.

How about this:

```java
    // Read from the last element to the end and make sure it's zeroed
    int endOfLastElement = HEADER_LENGTH + 1028 + 4 * (Element.HEADER_LENGTH + 1024);
    int readLength = (int) (queue.raf.length() - endOfLastElement);
    data = new byte[readLength];
    expected = new byte[readLength];
    queue.raf.seek(endOfLastElement);
    queue.raf.readFully(data, 0, readLength);
    assertThat(data).isEqualTo(expected);
```