prevent multi-transpose on pad

Author: RandySheriffH

tf2onnx/optimizer/transpose_optimizer.py

@@ -556,7 +556,7 @@ def _pad_handler(self, trans, node):
             new_pads = [pads[0], pads[3], pads[1], pads[2], pads[4], pads[7], pads[5], pads[6]]
             node.set_attr("pads", new_pads)
             return self._switch_transpose_and_node(node, trans)
-        if node.inputs[1].is_const():
+        if node.inputs[1].is_const() and self._nodes_has_single_consumer_node([node.inputs[1]]):
             pads = node.inputs[1].get_tensor_value()
             # NHWC->NCHW
             new_pads = np.array([pads[0], pads[3], pads[1], pads[2], pads[4], pads[7], pads[5], pads[6]],