Changing platform target results in flashing error message

I'm using VS 2017 15.3.2.

With this csproj:
```

Exe
net47

```

If I change Platform target (under Project Properties, Build), I get an error message that appears and then disappears:
```
Assets file '' doesn't have a target for '.NETFramework,Version=v4.7/win7-x64'. ENsure that restore has run and that you have included 'net47' in the TargetFramework for your project. You may also need to include 'win7-x64' in your project's RuntimeIdentifiers.
```

Reproduce the issue from the shown csproj by changing Platform target under Project Properties > Build. Start by tracing how that change triggers restore and displays the reported assets-file error. Done means changing the platform target no longer produces a flashing error message and the project remains in the expected restored state.

Written by the indexing model from the issue text.