bug fix: rmt can not exit when sync redis data to rdb files

[AlexStocks]

firstly, show my rmt.conf as follows:

[source]
type: single
servers:
-10.10.10.9:6379
-10.10.10.10:6380

[target]
type: rdb file

[common]
listen: 10.33.80.221:8888
step: 1
mbuf_size: 4096
source_safe: true
dir: data

When rmt completes its job, the rmt process suspended and did not halt. By rmt.log, I noticed that both the read thread read_thread_run and the write thread write_thread_run did not terminate when the rob files have been saved.

To use rmt, I clone a fork and try to modify it to let it run by my rmt.conf. But it can not run If the value of source_safe is false.

Hope u check my code and fix this bug. Thanks.