Rewrite comment

Signed-off-by: Nghia Truong <nghiatruong.vn@gmail.com>

cpp/include/cudf/detail/labeling/label_segments.cuh

@@ -65,7 +65,8 @@ void label_segments(InputIterator offsets_begin,
                     rmm::cuda_stream_view stream)
 {
   // If the output array is empty, that means we have all empty segments.
-  // In such cases, there will not be any label value to output.
+  // In such cases, we must terminate immediately. Otherwise, the for loop below may try to access
+  // memory of the output array, resulting in "illegal memory access" error.
   if (thrust::distance(out_begin, out_end) == 0) { return; }
 
   // When the output array is not empty, always fill it with `0` value first.