JAMES-3506 Avoid copies when reading byte buffers

[chibenwa]

https://docs.oracle.com/javase/7/docs/api/java/nio/ByteBuffer.html#hasArray()

Tells whether or not this buffer is backed by an accessible byte array.

If this method returns true then the array and arrayOffset methods may safely be invoked. 

https://docs.oracle.com/javase/7/docs/api/java/nio/ByteBuffer.html#array()

Returns the byte array that backs this buffer  (optional operation). 

As I understand that you feel concerned I will open a separated PR, But still want this code merged.