Generation fails for read-only controllers

[IanKemp]

PS C:\Users\<removed>\.nuget\packages\r4mvc.tools\1.0.0-ci-00377\tools> .\R4Mvc.Tools.exe generate -p "<path\to\removed>.csproj"
  R4Mvc Generator Tool v1.0.0-ci-00377

Using: Visual Studio Enterprise 2019 - 16.6.30320.27
Project: <path\to\removed>.csproj

Creating Workspace ...
Loading project ...
Compiling project ...
Detected MVC version: 3.1.0.0

Processing controller ControllerName

Unhandled Exception: System.UnauthorizedAccessException: Access to the path '<path\to\ControllerName>.cs' is denied.
   at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)
   at System.IO.FileStream.Init(String path, FileMode mode, FileAccess access, Int32 rights, Boolean useRights, FileShare share, Int32 bufferSize, FileOptions options, SECURITY_ATTRIBUTES secAttrs, String msgPath, Boolean bFromProxy, Boolean useLongPath, Boolean checkHost)
   at System.IO.FileStream..ctor(String path, FileMode mode, FileAccess access, FileShare share, Int32 bufferSize, FileOptions options, String msgPath, Boolean bFromProxy)
   at System.IO.FileStream..ctor(String path, FileMode mode)
   at R4Mvc.Tools.Services.FilePersistService.WriteFile(SyntaxNode fileTree, String filePath)
   at R4Mvc.Tools.Services.ControllerRewriterService.RewriteControllers(CSharpCompilation compiler)
   at R4Mvc.Tools.Commands.GenerateCommand.Runner.<Run>d__9.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at R4Mvc.Tools.Program.<Main>d__0.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at R4Mvc.Tools.Program.<Main>(String[] args)

It seems like the tool is trying to write to my controller's .cs file to mark it as partial, which fails because said file is read-only (we are sadly using TFS for version control, it checks out all files as read-only). FilePersistService should probably be updated to handle this read-only case.