fix pq distance calculation outofrange according to faiss suggests (#3925)

Signed-off-by: Nyangxuan <xuan.yang@zilliz.com>
Co-authored-by: Nyangxuan <xuan.yang@zilliz.com>

core/src/index/thirdparty/faiss/gpu/impl/PQCodeDistances-inl.cuh

@@ -52,6 +52,15 @@ pqCodeDistances(Tensor<float, 2, true> queries,
   auto subQuantizer = blockIdx.y;
 
 
+  // Each thread will load the pq centroid data for the code that it
+  // is processing
+  if(!loadingThreads) {
+#pragma unroll
+      for (int i = 0; i < DimsPerSubQuantizer; ++i) {
+        subQuantizerData[i] = pqCentroids[subQuantizer][i][code].ldg();
+      }
+  }
+
   // Where we store our query vector
   float* smemQuery = smem;
 
@@ -147,12 +156,6 @@ pqCodeDistances(Tensor<float, 2, true> queries,
         }
       } else {
 
-        // Each thread will load the pq centroid data for the code that it
-        // is processing
-        #pragma unroll
-        for (int i = 0; i < DimsPerSubQuantizer; ++i) {
-        subQuantizerData[i] = pqCentroids[subQuantizer][i][code].ldg();
-        }
 
         // These are the processing threads
         float dist = 0.0f;