fix NCHW converting bug when in pad_rewriter

Author: charlieguo0307

tf2onnx/rewriter/conv2d_with_pad_rewriter.py

@@ -43,10 +43,16 @@ def rewrite_conv2d_with_pad(g, ops):
         logger.debug("merge pad [%s] into conv [%s]", pad.name, conv.name)
         paddings_val = np.array(paddings.get_tensor_value())
         # can't pad on batch or channel dimensions
-        if np.any(paddings_val[0]) or np.any(paddings_val[3]):
-            continue
+        data_format = conv.get_attr("data_format").s.decode("utf-8")
+        if data_format == "NHWC":
+            if np.any(paddings_val[0]) or np.any(paddings_val[3]):
+                continue
+            paddings_val = paddings_val[1:3]
+        else:
+            if np.any(paddings_val[0]) or np.any(paddings_val[1]):
+                continue
+            paddings_val = paddings_val[2:4]
 
-        paddings_val = paddings_val[1:3]
         paddings_val = paddings_val.transpose().flatten()
         g.replace_input(conv, conv.input[0], pad.input[0])
         # convert Conv2D