[vcpkg] Show Empty Object on vcpkg --list when used with --x-json (mi…

…crosoft#13667)

Thanks to @strega-nil for recommending using Json::stringify over my initial idea of simply printing an empty object

Closes microsoft#13637

src/vcpkg/commands.list.cpp

@@ -95,7 +95,10 @@ namespace vcpkg::Commands::List
 
         if (installed_ipv.empty())
         {
-            System::print2("No packages are installed. Did you mean `search`?\n");
+            if (args.output_json())
+                System::print2(Json::stringify(Json::Object(), {}));
+            else
+                System::print2("No packages are installed. Did you mean `search`?\n");
             Checks::exit_success(VCPKG_LINE_INFO);
         }