fix custom operator backward=None (#48656)

Author: jiahy0825

paddle/fluid/eager/custom_operator/custom_operator_node.cc

@@ -217,18 +217,20 @@ RunCustomOpNode::operator()(
   VLOG(6) << "Prepare Grad outputs for size: " << grad_outputs_names.size();
   for (size_t i = 0; i < OutputMeta().size(); i++) {
     if (map[0][0].find(i) != map[0][0].end()) {
+      int grad_output_idx = map[0][0][i];
       VLOG(7) << "Insert grad outputs: " << i
-              << " with size: " << OutputMeta()[i].size()
-              << " to tmp_outputs: " << map[0][0][i];
-      for (size_t j = 0; j < OutputMeta()[i].size(); j++) {
-        outs[i].emplace_back(/* init it incase of copy nullptr of shared_ptr */
-                             std::make_shared<phi::DenseTensor>(
-                                 phi::DataType::UNDEFINED),
-                             egr::Controller::Instance().GenerateUniqueName(
-                                 "custom_tmp_grad"));
-        egr::EagerUtils::autograd_meta(&(outs[i][j]));
+              << " with size: " << OutputMeta()[grad_output_idx].size()
+              << " to tmp_outputs: " << grad_output_idx;
+      for (size_t j = 0; j < OutputMeta()[grad_output_idx].size(); j++) {
+        outs[grad_output_idx]
+            .emplace_back(/* init it incase of copy nullptr of shared_ptr */
+                          std::make_shared<phi::DenseTensor>(
+                              phi::DataType::UNDEFINED),
+                          egr::Controller::Instance().GenerateUniqueName(
+                              "custom_tmp_grad"));
+        egr::EagerUtils::autograd_meta(&(outs[grad_output_idx][j]));
       }
-      tmp_outs[map[0][0][i]] = outs[i];
+      tmp_outs[grad_output_idx] = outs[grad_output_idx];
     }
   }
   for (size_t i = 0; i < tmp_outs.size(); i++) {