Prevent updating to unpublished/unlisted NuGet packages.

Update-Package was updating to unpublished/unlisted NuGet packages.

src/AddIns/Misc/PackageManagement/Project/Src/ProcessPackageAction.cs

@@ -136,7 +136,7 @@ namespace ICSharpCode.PackageManagement
 		{
 			Package = Project
 				.SourceRepository
-				.FindPackage(PackageId, PackageVersion, AllowPrereleaseVersions, allowUnlisted: true);
+				.FindPackage(PackageId, PackageVersion, AllowPrereleaseVersions, allowUnlisted: false);
 		}
 		
 		void ThrowPackageNotFoundError(string packageId)

src/AddIns/Misc/PackageManagement/Test/Src/InstallPackageActionTests.cs

@@ -385,6 +385,7 @@ namespace PackageManagement.Tests
 			FakePackage expectedPackage = fakeProject.FakeSourceRepository.AddFakePackageWithVersion("test", "1.0");
 			expectedPackage.Listed = false;
 			action.PackageId = "test";
+			action.PackageVersion = new SemanticVersion("1.0");
 			
 			action.Execute();
 			
@@ -392,6 +393,19 @@ namespace PackageManagement.Tests
 			Assert.AreEqual(expectedPackage, actualPackage);
 		}
 		
+		[Test]
+		public void Execute_InstallUnlistedPackageWithoutVersion_DoesNotInstallPackageIntoProject()
+		{
+			CreateAction();
+			FakePackage expectedPackage = fakeProject.FakeSourceRepository.AddFakePackageWithVersion("test", "1.0");
+			expectedPackage.Listed = false;
+			action.PackageId = "test";
+			
+			Exception ex = Assert.Throws(typeof(ApplicationException), () => action.Execute());
+			
+			Assert.AreEqual("Unable to find package 'test'.", ex.Message);
+		}
+		
 		[Test]
 		public void Execute_PackageIdSpecifiedButDoesNotExistInRepository_ExceptionThrown()
 		{