Item Function doesn’t accept Item Metadata batching

_Reported internally by email._

### Steps to reproduce

Either include a project sample, attach a zipped project, or provide IDE / CLI steps to create the project and repro the behaviour. Example of a project sample:

Project file
```xml

c_pch.h

c_pch.h

c_pch.h

Create
$(IntDir)%(ClCompile.PrecompiledHeaderFile).pch

```

```
C:\Test>msbuild test.proj
Microsoft (R) Build Engine version 15.9.20+g88f5fadfbe for .NET Framework
Copyright (C) Microsoft Corporation. All rights reserved.

Build started 11/8/2018 5:03:08 PM.
Project "C:\Test\test.proj" on node 1 (default targets).
Start:
c_pch.h =- -1
c_pch.h =- 0
```