Fix OnPlatform-like extensions with a single input parameter

src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlOptionMarkupExtensionTransformer.cs

@@ -366,6 +366,7 @@ internal class AvaloniaXamlIlOptionMarkupExtensionTransformer : IXamlAstTransfor
             foreach (var branch in ExtensionNodeContainer.Branches)
             {
                 var next = codeGen.DefineLabel();
+                codeGen.Emit(OpCodes.Nop);
                 if (branch.HasContext)
                 {
                     codeGen.Ldloc(context.ContextLocal);

tests/Avalonia.Markup.Xaml.UnitTests/MarkupExtensions/OptionsMarkupExtensionTests.cs

@@ -434,7 +434,7 @@ public class OptionsMarkupExtensionTests : XamlTestBase
 <TextBlock xmlns='https://github.com/avaloniaui'
            xmlns:local='clr-namespace:Avalonia.Markup.Xaml.UnitTests.MarkupExtensions;assembly=Avalonia.Markup.Xaml.UnitTests'
            xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'
-           Text='{local:OptionsMarkupExtensionNoServiceProvider OptionB=""Im Option 2""}' />";
+           Text='{local:OptionsMarkupExtensionNoServiceProvider OptionB=""Im Option 2"", OptionA=""Im Option 1""}' />";
 
         var textBlock = (TextBlock)AvaloniaRuntimeXamlLoader.Load(xaml);