close model if not null

src/main/java/plugins/danyfel80/tensorflow/v1/Tensorflow1Interface.java

@@ -132,9 +132,10 @@ public class Tensorflow1Interface implements DeepLearningInterface
 	@Override
 	public void closeModel() {
 		sig = null;
-		model.session().close();
-		if (model != null)
+		if (model != null) {
+			model.session().close();
 			model.close();
+		}
 		model = null;
 		
 	}