[Bug]: fail to search with hints=iterative_filter if expression is empty

[yanliang567]

Is there an existing issue for this?

• I have searched the existing issues

Environment

- Milvus version: master-20250106-731e882d-amd64
- Deployment mode(standalone or cluster): standalone
- MQ type(rocksmq, pulsar or kafka):    
- SDK version(e.g. pymilvus v2.0.0rc2): 2.6.0rc49

Current Behavior

fail to search with hint="iterative_filter" if the expr="", error:
pymilvus.exceptions.MilvusException: <MilvusException: (code=65535, message=fail to search on QueryNode 1: worker(1) query failed: ReduceSearchResultsAndFillData failed: Assert "search_result->seg_offsets_.size() == nq * topK" => wrong seg offsets size, size = 0, expected size = 4000 at /workspace/source/internal/core/src/segcore/reduce/Reduce.cpp:80

Expected Behavior

ignore or return a meaningful msg

Steps To Reproduce

search with hint="iterative_filter" and expr=""

Milvus Log

No response

Anything else?

No response

[yanliang567]

/assign @chasingegg
/unassign

[XuanYang-cn]