Always initialize PartitionBoundInfoData's null_index.
Always initialize PartitionBoundInfoData's null_index.

This doesn't actually matter at present, because the current code
never consults null_index for range partitions.  However, leaving
it uninitialized is still a bad idea, so let's not do that.

Amul Sul, reviewed by Ashutosh Bapat

Discussion: 44989721a34e8e62dc82379c5f9d924ea9f53892@mail.gmail.com

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