fix add grad bug test=develop (#22924)

* fix add grad bug test=develop

* update style test=develop

python/paddle/fluid/incubate/fleet/parameter_server/pslib/optimizer_factory.py

@@ -189,6 +189,12 @@ class DistributedAdam(DistributedOptimizerImplBase):
         sparse_table_index = 0
         for loss in losses:
             prog_id = str(id(loss.block.program))
+            # param_grads of program
+            params_grads = sorted(
+                fluid.backward.append_backward(loss, parameter_list,
+                                               no_grad_set),
+                key=lambda x: x[0].name)
+
             if prog_id not in program_id_set:
                 program_id_set.add(prog_id)
                 sparse_table = self._find_multi_distributed_lookup_table([loss])
@@ -215,11 +221,6 @@ class DistributedAdam(DistributedOptimizerImplBase):
                     loss.block.program, sparse_table)
                 prog_id_to_sparse_grads[prog_id] = grads_dict
 
-            # param_grads of program
-            params_grads = sorted(
-                fluid.backward.append_backward(loss, parameter_list,
-                                               no_grad_set),
-                key=lambda x: x[0].name)
             if prog_id not in prog_id_to_param_grads:
                 prog_id_to_param_grads[prog_id] = []
             prog_id_to_param_grads[prog_id].append(params_grads)