msbuild: MSBuild /t:Restore exit code is always 0

From @Jonathan34 on May 10, 2017 21:41

Steps to reproduce

• have an invalid csproj:

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFramework>netcoreapp2.0</TargetFramework>
    <!--<RuntimeFrameworkVersion>2.0.0-preview1-005957-00</RuntimeFrameworkVersion>-->
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.0.0" />
    <PackageReference Include="xunit" Version="2.3.0-beta2-build3683" />
    <PackageReference Include="xunit.runner.visualstudio" Version="2.3.0-beta2-build1317" />
    <PackageReference Include="Microsoft.AspNetCore.TestHost" Version="1.1.2" />
  </ItemGroup>
  <ItemGroup>
    <ProjectReference Include="..\..\src\API.csproj"></ProjectReference>
  </ItemGroup>
  <ItemGroup>
    <Service Include="{82a7f48d-3b50-4b1e-b82e-3ada8210c358}" />
  </ItemGroup>
</Project>Invalid Characters to fail processing of the project file

then dotnet restore

Expected behavior

/app/code/test/IntegrationTests/IntegrationTests.csproj(18,11): error MSB4025: The project file could not be loaded. Data at the root level is invalid. Line 18, position 11
.
exit code is not 0

Actual behavior

exit code is 0

Environment data

dotnet --info output:

.NET Command Line Tools (2.0.0-preview1-005957)

Product Information:
 Version:            2.0.0-preview1-005957
 Commit SHA-1 hash:  056ac0e9cd

Runtime Environment:
 OS Name:     Mac OS X
 OS Version:  10.12
 OS Platform: Darwin
 RID:         osx.10.12-x64
 Base Path:   /usr/local/share/dotnet/sdk/2.0.0-preview1-005957/

Microsoft .NET Core Shared Framework Host

  Version  : 2.0.0-preview1-002111-00
  Build    : 1ff021936263d492539399688f46fd3827169983

Copied from original issue: dotnet/cli#6569