[Bug-fix][Broker-load] Fix the bug of the label already exists when the txn has been finished

**Describe the bug**
The load job has been cancelled by label already exists while there are no finished load job with the same name.

**To Reproduce**
1. create a load job
2. load job hang on committed
3. restart fe
4. the txn of load job is visible
5. while the load job is cancelled by label already exists

**Expected behavior**
The load job is finished correctly.

