Warning to have both FP16 and FP32 models

[unreal79]

I deleted 1 Gb "C:\Program Files\paint.net\Effects\BackgroundRemover\onnx\RMBG-2.0_FP32.onnx" file because I believe FP16 model is enough for my needs, but upon starring Paint.NET and running your plugin, I'm getting warning/error. Still, background removing works fine (with FP16 model).

I think upon discovery of a missed onnx model, the plugin should set option to use FP16 (or make the option inactive).