[SPARK-2415] [SQL] RowWriteSupport should handle empty ArrayType correctly.

`RowWriteSupport` doesn't write empty `ArrayType` value, so the read value becomes `null`.
It should write empty `ArrayType` value as it is.

Author: Takuya UESHIN <ueshin@happy-camper.st>

Closes #1339 from ueshin/issues/SPARK-2415 and squashes the following commits:

32afc87 [Takuya UESHIN] Merge branch 'master' into issues/SPARK-2415
2f05196 [Takuya UESHIN] Fix RowWriteSupport to handle empty ArrayType correctly.