Code fix for VSTHRD103 doesn't handle nested awaits properly

#### Repro steps

```csharp
await Task.Run(() => Console.Error).Result.WriteLineAsync();
```

#### Expected behavior

```csharp
await (await Task.Run(() => Console.Error)).WriteLineAsync();
```

#### Actual behavior

```csharp
await await Task.Run(() => Console.Error);
```

- Version used: 15.8.132
- Application (if applicable): VS 15.8 Preview 5
