Preprocessing invalid file fails to display errors

### Steps to reproduce
Project file (DotNetCoreTestApp.csproj)
```xml
INVALID XML FILE

Exe
netcoreapp2.1

```

Directory contents:
```
/
- DotNetCoreTestApp.csproj
```

Command line
```
dotnet msbuild /pp:msbuild.xml DotNetCoreTestApp.csproj
```
### Expected behavior
The command should print an error message to stderror or stdout.

### Actual behavior
No output is printed at all. The output file is created but empty. Exit code is 1.
For comparison, this is the output from an older version of msbuild.exe:
```
DotNetCoreTestApp.csproj(1,1): error MSB4025: The project file could not be loaded. Data at the root level is invalid. Line 1, position 1.
```

### Environment data
`dotnet msbuild /version` output:
Microsoft (R) Build Engine version 15.9.20+g88f5fadfbe for .NET Core
Copyright (C) Microsoft Corporation. All rights reserved.

15.9.20.62856