Fix auto growth bug of optimizer in dygraph mode

test=develop

python/paddle/fluid/optimizer.py

@@ -275,6 +275,17 @@ class Optimizer(object):
         self._create_global_learning_rate()
 
         optimize_ops = []
+        if framework._in_dygraph_mode():
+            for param_and_grad in parameters_and_grads:
+                if param_and_grad[1] is None:
+                    continue
+                with param_and_grad[0].block.program._optimized_guard(
+                        param_and_grad):
+                    if param_and_grad[0].trainable is True:
+                        optimize_op = self._append_optimize_op(global_block,
+                                                               param_and_grad)
+                        optimize_ops.append(optimize_op)
+        else:
             for param_and_grad in parameters_and_grads:
                 if param_and_grad[1] is None:
                     continue