`GeneratorDriver.GetRunResult()` should not throw

[chsienki]

`GeneratorDriver.GetRunResult()` should not throw

[Peter-Juhasz]

Is this the same as this one I encountered in VS 17.11.0 P2?

StreamJsonRpc.RemoteInvocationException: Object reference not set to an instance of an object.
   at StreamJsonRpc.JsonRpc.<InvokeCoreAsync>d__154`1.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 System.Threading.Tasks.ValueTask`1.get_Result()
   at Microsoft.CodeAnalysis.Remote.BrokeredServiceConnection`1.<TryInvokeAsync>d__18`1.MoveNext()
RPC server exception:
System.NullReferenceException: Object reference not set to an instance of an object.
      at Microsoft.CodeAnalysis.GeneratorDriver.<GetRunResult>g__getGeneratorSources|15_1(GeneratorState generatorState)
      at Microsoft.CodeAnalysis.GeneratorDriver.<>c.<GetRunResult>b__15_0(ISourceGenerator generator, GeneratorState generatorState)
      at Microsoft.CodeAnalysis.ImmutableArrayExtensions.ZipAsArray[T1,T2,TResult](ImmutableArray`1 self, ImmutableArray`1 other, Func`3 map)
      at Microsoft.CodeAnalysis.GeneratorDriver.GetRunResult()
      at Microsoft.CodeAnalysis.SolutionCompilationState.CompilationTracker.GetSourceGeneratorDiagnosticsAsync(SolutionCompilationState compilationState, CancellationToken cancellationToken)
      at Microsoft.CodeAnalysis.Remote.RemoteDiagnosticAnalyzerService.<>c__DisplayClass4_0.<<GetSourceGeneratorDiagnosticsAsync>b__0>d.MoveNext()
   --- End of stack trace from previous location ---
      at Microsoft.CodeAnalysis.Remote.RemoteWorkspace.<>c__DisplayClass7_0`1.<<RunWithSolutionAsync>g__ProcessSolutionAsync|1>d.MoveNext()
   --- End of stack trace from previous location ---
      at Microsoft.CodeAnalysis.Remote.RemoteWorkspace.RunWithSolutionAsync[T](AssetProvider assetProvider, Checksum solutionChecksum, Boolean updatePrimaryBranch, Func`2 implementation, CancellationToken cancellationToken)
      at Microsoft.CodeAnalysis.Remote.RemoteWorkspace.RunWithSolutionAsync[T](AssetProvider assetProvider, Checksum solutionChecksum, Boolean updatePrimaryBranch, Func`2 implementation, CancellationToken cancellationToken)
      at Microsoft.CodeAnalysis.Remote.BrokeredServiceBase.RunWithSolutionAsync[T](Checksum solutionChecksum, Func`2 implementation, CancellationToken cancellationToken)
      at Microsoft.CodeAnalysis.Remote.RemoteDiagnosticAnalyzerService.GetSourceGeneratorDiagnosticsAsync(Checksum solutionChecksum, ProjectId projectId, CancellationToken cancellationToken)