non-sense segment is been generated

[chaoyli]

When doing schema change, error occurs when flushing segment.

[chaoyli]

Segment which size reaches OLAP_MAX_COLUMN_SEGMENT_FILE_SIZE will be flushed into disk. If the previous segment reach the threshold just right, and been flushed into disk. The following finalize() when closing ColumnDataWriter will generate a non-sense segment. In this scenario, undefined behavior will happens.