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ARROW-6268: [Java] Empty buffers to have a valid address.

- As part of arrow buffer refactoring done earlier, the empty buffers are now created with an invalid addresses.
- This breaks client code that assumed that even empty buffers are valid.
- Uses the address of EMPTY buffer from allocation manager.

Closes #5103 from praveenbingo/testEmptyBuf and squashes the following commits:

464e81c76 <Praveen> ARROW-6268:  Empty buffers to have a valid address.

Authored-by: Praveen <praveen@dremio.com>
Signed-off-by: Praveen <praveen@dremio.com>