[C++] Write serializer could be crash if the value buffer is empty

### Describe the bug, including details regarding any error messages, version, and platform.

`WriteArrowSerialize` could unconditionally read values from the Arrow array even for null rows. Since it's possible the caller could provided a zero-sized dummy buffer for all-null arrays, this caused an ASAN heap-buffer-overflow.

### Component(s)

Parquet