Partition split hung

## Bug Report

Please answer these questions before submitting your issue. Thanks!

1. What did you do?
Create a table with 8 partitions
Write some data to the table
Start partition split

2. What did you expect to see?
The partition split can be completed successfully.

3. What did you see instead?
The partitions are in `SPLITTING` state, the process hung and could not response requests

4. What version of Pegasus are you using?
2.4

Reproduce the report on Pegasus 2.4 by creating a table with 8 partitions, writing data, and starting a partition split. Observe the partitions in SPLITTING state and the unresponsive requests; done means the split completes successfully and requests continue responding.

Written by the indexing model from the issue text.