Fix bmp bp reorder (#2543)

### What problem does this PR solve?

Fix bmp BlockFwd::GetFwd, when GetFwd is called with doc_num that is not
actual doc num. This may happen when call bp_reorder optimization.

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)
- [x] Test cases

python/test_pysdk/test_knn.py

@@ -1069,7 +1069,7 @@ def test_sparse_knn_with_index(self, check_data, suffix):
                                                index.IndexType.BMP,
                                                {"block_size": "8", "compress_type": "compress"}), ConflictType.Error)
 
-        table_obj.optimize("idx1", {"topk": "3"})
+        table_obj.optimize("idx1", {"topk": "3", "bp_reorder": ""})
 
         res, extra_result = (table_obj
                              .output(["*", "_row_id", "_similarity"])

src/storage/knn_index/sparse/bmp_alg.cppm

@@ -265,10 +265,13 @@ public:
     void Optimize(const BMPOptimizeOptions &options) {
         std::unique_lock lock(mtx_);
 
-        if (options.bp_reorder_) {
+        while (options.bp_reorder_) {
             SizeT block_size = this->block_fwd_.block_size();
             SizeT term_num = this->bm_ivt_.term_num();
             SizeT doc_num = this->doc_ids_.size() - this->doc_ids_.size() % block_size;
+            if (doc_num == 0) {
+                break;
+            }
 
             this->bm_ivt_ = BMPIvt<DataType, CompressType, BMPOwnMem::kTrue>(term_num);
             Vector<Pair<Vector<IdxType>, Vector<DataType>>> fwd = this->block_fwd_.GetFwd(doc_num, term_num);
@@ -293,6 +296,7 @@ public:
                 SparseVecRef<DataType, IdxType> doc((i32)indices.size(), indices.data(), data.data());
                 this->AddDoc(doc, doc_ids[i], false);
             }
+            break;
         }
         if (options.topk_ != 0) {
             SizeT term_num = this->bm_ivt_.term_num();

src/storage/knn_index/sparse/bmp_fwd.cppm

@@ -441,6 +441,9 @@ public:
                 const auto &[term_id, block_size, block_offsets, scores] = iter.Value();
                 for (SizeT i = 0; i < block_size; ++i) {
                     BMPDocID doc_id = block_offsets[i] + block_id * block_size_;
+                    if (doc_id >= doc_num) {
+                        break;
+                    }
                     DataType score = scores[i];
                     fwd[doc_id].first.push_back(term_id);
                     fwd[doc_id].second.push_back(score);