[UWP Renderer] Allow nested fallbacks

source/uwp/SharedRenderer/lib/XamlBuilder.cpp

@@ -302,7 +302,18 @@ namespace AdaptiveCards::Rendering::Xaml_Rendering
                     throw ex;
                 }
 
-                std::tie(newControl, renderedElement) = XamlHelpers::RenderFallback(element, renderContext, renderArgs);
+                try
+                {
+                    std::tie(newControl, renderedElement) = XamlHelpers::RenderFallback(element, renderContext, renderArgs);
+                }
+                catch (winrt::hresult_error const& ex)
+                {
+                    // if we get an E_PERFORM_FALLBACK error again, we should only throw it if `ancestorHasFallBack`
+                    if (ex.code() != E_PERFORM_FALLBACK || (ex.code() == E_PERFORM_FALLBACK && ancestorHasFallback))
+                    {
+                        throw ex;
+                    }
+                }
             }
 
             // If we got a control, add a separator if needed and the control to the parent panel

source/uwp/SharedRenderer/lib/XamlHelpers.cpp

@@ -333,15 +333,28 @@ namespace AdaptiveCards::Rendering::Xaml_Rendering::XamlHelpers
 
             if (fallbackElementRenderer)
             {
-                fallbackControl = fallbackElementRenderer.Render(fallbackElement, renderContext, renderArgs);
-
-                renderedElement = fallbackElement;
+                try
+                {
+                    fallbackControl = fallbackElementRenderer.Render(fallbackElement, renderContext, renderArgs);
+                    renderedElement = fallbackElement;
+                }
+                catch (winrt::hresult_error const& ex)
+                {
+                    if (ex.code() == E_PERFORM_FALLBACK)
+                    {
+                        std::tie(fallbackControl, renderedElement) = RenderFallback(fallbackElement, renderContext, renderArgs);
+                    }
+                    else
+                    {
+                        throw(ex);
+                    }
+                }
             }
-
-            if (!fallbackControl)
+            else
             {
                 std::tie(fallbackControl, renderedElement) = RenderFallback(fallbackElement, renderContext, renderArgs);
             }
+
             fallbackHandled = true;
             break;
         }