Solve invalid memory read issue in find_nearest (#112)

This PR addresses the corner cases where neighbor id may be
[max](https://github.com/intel/ScalableVectorSearch/blob/72633231807d46ff59f651916858fa0ed6ba3ee4/include/svs/lib/neighbor.h#L160)
when distance is infinity. In such scenarios, the system could return a
neighbor with the maximum ID, leading to an invalid memory read. To
resolve this, the PR modifies the behavior to reset the ID to the first
index, ensuring a valid existing neighbor is returned.

Author: Dian-Lun (Aaron) Lin

include/svs/core/kmeans.h

@@ -45,6 +45,12 @@ Neighbor<size_t> find_nearest(const Query& query, const Data& data) {
         auto d = distance::compute(f, query, data.get_datum(i));
         nearest = std::min(nearest, Neighbor<size_t>(i, d));
     }
+
+    // The case where the distance is infinity and the id remains unchanged from sentinel_v,
+    // reset to the first index to return to the exsiting neighbor.
+    if (nearest.id() >= data.size()) {
+        nearest = Neighbor<size_t>(0, nearest.distance());
+    }
     return nearest;
 }