[C#] Regression on 0.5.0 with DML

**Describe the bug**
C# Version 0.5.0 broke DML models, such as microsoft--Phi-3-mini-4k-instruct-onnx directml-int4-awq-block-128.
The model loads, but the Generator's constructor throws an Access violation exception.

**To Reproduce**
Steps to reproduce the behavior:
1. Try running [Phi3 Sample](https://github.com/microsoft/onnxruntime-genai/tree/main/examples/csharp/HelloPhi) with DML
2. Exception line [98](https://github.com/microsoft/onnxruntime-genai/blob/main/examples/csharp/HelloPhi/Program.cs#L98)

**Expected behavior**
Works just as 0.4.0.

**Desktop (please complete the following information):**
- OS: Windows 11 (24H2)

Start with examples/csharp/HelloPhi/Program.cs at line 98 and reproduce the Phi-3 sample using DML on Windows 11. Compare the C# Generator construction and relevant behavior between versions 0.4.0 and 0.5.0; done means the DML model loads and the sample runs without an Access violation.

Written by the indexing model from the issue text.