Fix MakeContiguous sample_dim for empty batches. (#5567)

Use TensorLists's sample_dim instead of the one from (potentially nonexistent) sample 0.

Signed-off-by: Michał Zientkiewicz <[email protected]>

Author: mzient

dali/pipeline/operator/builtin/make_contiguous.cu

@@ -21,7 +21,7 @@ namespace dali {
 
 void MakeContiguousMixed::RunImpl(Workspace &ws) {
   const auto& input = ws.Input<CPUBackend>(0);
-  int sample_dim = input[0].shape().sample_dim();
+  int sample_dim = input.shape().sample_dim();
   size_t batch_size = input.num_samples();
   DALIDataType type = input.type();
   size_t type_size = input.type_info().size();