AssimpContext.ExportFile broken

Using ExportFile method always results to a crash, regardless the format I am exporting to:
`using var ctx = new AssimpContext();
ctx.ExportFile(new Scene(), fileName, "obj");
`

Exception:
`System.AccessViolationException: 'Attempted to read or write protected memory. This is often an indication that other memory is corrupt.'
`

I am using .Net Core 3.1 and AssimpNet 4.1.0.

No source files or tests are named. Reproduce the provided .NET Core 3.1 example with AssimpNet 4.1.0, then trace AssimpContext.ExportFile through the native export boundary. Done means exporting the sample Scene no longer raises AccessViolationException.

Written by the indexing model from the issue text.