If EmitNuSpec=false, don't set NuspecFile so that Pack does not write the nuspec

Author: kzu

src/Build/NuGet.Build.Packaging.Tasks/NuGet.Build.Packaging.targets

@@ -38,7 +38,8 @@ Copyright (c) .NET Foundation. All rights reserved.
 
 		<!-- Whether to emit the nuspec that's used to create the final package -->
 		<EmitNuSpec Condition="'$(EmitNuSpec)' == ''">false</EmitNuSpec>
-		<NuspecFile Condition="'$(NuspecFile)' == ''">$(OutputPath)\$(PackageId).nuspec</NuspecFile>
+		<!-- Only default the nuspec file if we are supposed to emit one. -->
+		<NuspecFile Condition="'$(NuspecFile)' == '' and '$(EmitNuSpec)' == 'true'">$(OutputPath)\$(PackageId).nuspec</NuspecFile>
 	</PropertyGroup>
 
 	<Import Project="NuGet.Build.Packaging.Inference.targets" Condition="'$(InferPackageContents)' != 'false'" />
@@ -373,9 +374,6 @@ Copyright (c) .NET Foundation. All rights reserved.
 	-->
 	<Target Name="Pack" DependsOnTargets="$(PackDependsOn)" Returns="@(PackageTargetPath)" Condition="'$(IsPackable)' == 'true'">
 		<MakeDir Directories="$(PackageOutputPath)" Condition="!Exists('$(PackageOutputPath)')" />
-		<PropertyGroup>
-			<NuspecFile Condition="'$(EmitNuspec)' == 'true' And '$(NuspecFile)' == ''">$(OutputPath)\$(PackageId).nuspec</NuspecFile>
-		</PropertyGroup>
 		<CreatePackage Manifest="@(PackageTargetPath)" NuspecFile="$(NuspecFile)" Contents="@(_PackageContent)" TargetPath="@(PackageTargetPath->'%(FullPath)')">
 			<Output TaskParameter="OutputPackage" ItemName="_PackageTargetPath" />
 			<Output TaskParameter="OutputPackage" ItemName="FileWrites" />
@@ -402,4 +400,4 @@ Copyright (c) .NET Foundation. All rights reserved.
 	<Import Project="NuGet.Build.Packaging.Authoring.targets" Condition="'$(IsPackagingProject)' == 'true'" />
 	<Import Project="NuGet.Build.Packaging.CrossTargeting.targets" Condition="'$(IsCrossTargetingBuild)' == 'true' And '$(FromPackagingProject)' == 'true'" />
 	<Import Project="NuGet.Build.Packaging.Legacy.targets" />
-</Project>
+</Project>