Fall back to non optimized model proto

Fixes a bug where if the transpose optimizer fails, the proto will not be written.

Author: csteegz

tf2onnx/convert.py

@@ -101,7 +101,9 @@ def main():
                              input_names=args.inputs,
                              output_names=args.outputs,
                              inputs_as_nchw=args.inputs_as_nchw)
-
+ 
+    model_proto = g.make_model("converted from {}".format(args.input))
+        
     new_model_proto = GraphUtil.opt_transposes_with_graph(g, "converted from {}".format(args.input),
                                                           optimize=not args.continue_on_error)
     if new_model_proto: