prevent rebuilding artifacts in package stage (#931)

Author: mtfriesen

src/nuget/nuget.vcxproj

@@ -6,7 +6,7 @@
     <UndockedType>none</UndockedType>
   </PropertyGroup>
   <Import Project="$(SolutionDir)src\xdp.cpp.props" />
- <ItemGroup Condition="'$(BuildStage)' != 'AllPackage'">
+ <ItemGroup Condition="'$(BuildStage)' != 'Package' AND '$(BuildStage)' != 'AllPackage'">
     <ProjectReference Include="$(SolutionDir)src\bpfexport\bpfexport.vcxproj">
       <Project>{8f8830ff-1648-4772-87ed-f5da091fc931}</Project>
       <Private>false</Private>