Exception while inferencing ML.NET ONNX model that uses TextFeatures

[ppampati]

### System information

• OS version/distro: Windows 10
• .NET Version (eg., dotnet --info): .NET Core 3.1

Issue

• **What did you do?
  Trained a Fast tree model on text data.
  Saved the trained model to ONNX format
  Load the ONNX model and run Prediction
• **What happened?
  Prediction code threw an exception and application crashed.
• What did you expect?
  Prediction code to return score and predict label.
  Sample code is attached
  MLNetONNXSample.zip

Source code / logs

Please paste or attach the code or logs or traces that would be helpful to diagnose the issue you are reporting.

[Lynx1820]

This issue was resolved with PR #5435.