How large is bb.readableBytes generally? How do we guarantee that we never have two consecutive byte buffers that do not contain a '\n'?

Here's a failing test I wrote to show that seeing two consecutive buffers that do not contain a '\n' will break things.
```
    @Test
    public void testMultiplePartialBuffersConsecutively() {
        final byte[] buf0 = new byte[] {116,104};
        final byte[] buf1 = new byte[] {105,115};
        final byte[] buf2 = new byte[] {(int)'\n',119, 111, 114, 107, 115};

        List<byte[]> input = new ArrayList<byte[]>() {{
            add(buf0);
            add(buf1);
            add(buf2);
        }};
        List<CharSequence> expected = new ArrayList<CharSequence>() {{
            for (CharSequence s : "this works".split(" ", -1))
                add(s);
        }};

        List<CharSequence> actual = StringListBuilder.buildStrings(input);
        assertSameList(expected, actual);
    }
```