fix log_softmax if any dimension is 0-d (#34635)

paddle/fluid/operators/log_softmax_op.h

@@ -131,9 +131,11 @@ class LogSoftmaxKernel : public framework::OpKernel<T> {
     // allocate memory on device.
     Out->mutable_data<T>(context.GetPlace());
 
+    if (X->numel() != 0) {
       LogSoftmaxFunctor<DeviceContext, T>()(
           context.template device_context<DeviceContext>(), X, Out, axis);
     }
+  }
 };
 
 template <typename DeviceContext, typename T>
@@ -183,8 +185,11 @@ class LogSoftmaxGradKernel : public framework::OpKernel<T> {
     // allocate memory on device.
     dX->mutable_data<T>(context.GetPlace());
 
+    if (Out->numel() != 0) {
       LogSoftmaxGradFunctor<DeviceContext, T>()(
-        context.template device_context<DeviceContext>(), Out, dOut, dX, axis);
+          context.template device_context<DeviceContext>(), Out, dOut, dX,
+          axis);
+    }
   }
 };