LP #1609669: pt-table-checksum endless loop

**Reported in Launchpad by deng last update 28-02-2017 04:17:28

when the talbe is empty , pt-table-checksum will go on forever .
DEBUG:

1. pt_table_checksum:11365 6883 SELECT MAX(chunk) FROM `percona`.`checksums` WHERE db='mysql' AND tbl='columns_priv' AND master_crc IS NOT NULL
2. pt_table_checksum:11383 6883 Getting last checksum on Flume_kafka
3. pt_table_checksum:11386 6883 Flume_kafka max chunk: undef
4. pt_table_checksum:11439 6883 Sleep 0.25 waiting for chunks
5. pt_table_checksum:11383 6883 Getting last checksum on Flume_kafka
6. pt_table_checksum:11386 6883 Flume_kafka max chunk: undef
7. pt_table_checksum:11439 6883 Sleep 0.5 waiting for chunks
8. pt_table_checksum:11383 6883 Getting last checksum on Flume_kafka
9. pt_table_checksum:11386 6883 Flume_kafka max chunk: undef
10. pt_table_checksum:11439 6883 Sleep 0.75 waiting for chunks
11. pt_table_checksum:11383 6883 Getting last checksum on Flume_kafka
12. pt_table_checksum:11386 6883 Flume_kafka max chunk: undef
13. pt_table_checksum:11439 6883 Sleep 1 waiting for chunks
14. pt_table_checksum:11383 6883 Getting last checksum on Flume_kafka
15. pt_table_checksum:11386 6883 Flume_kafka max chunk: undef
16. pt_table_checksum:11439 6883 Sleep 1.25 waiting for chunks
17. pt_table_checksum:11383 6883 Getting last checksum on Flume_kafka
18. pt_table_checksum:11386 6883 Flume_kafka max chunk: undef
19. pt_table_checksum:11439 6883 Sleep 1.25 waiting for chunks
20. pt_table_checksum:11383 6883 Getting last checksum on Flume_kafka
21. pt_table_checksum:11386 6883 Flume_kafka max chunk: undef
22. pt_table_checksum:11439 6883 Sleep 1.25 waiting for chunks