Fix IDIC casts to invalid WinRT interfaces (#1659)

* Add catch to helper type check to catch exceptions if not winrt type rather than crashing

* Try alternative solution to do a WinRT type check

* Add test

src/Tests/FunctionalTests/DynamicInterfaceCasting/Program.cs

@@ -38,10 +38,26 @@
 IList<List<Point>> list2 = new List<List<Point>>();
 instance2.IterableOfPointIterablesProperty = list2;
 
+// Ensure that these don't crash but return null
+if ((IWinRTObject)instance as IList<Point> != null)
+{
+ return 105;
+}
+
+if ((IWinRTObject)instance as IList<ManagedClass> != null)
+{
+ return 106;
+}
+
 return 100;
 
 object SetAndGetBoxedValue(TestComponentCSharp.Class instance, object val)
 {
  instance.ObjectProperty = val;
  return instance.ObjectProperty;
 }
+
+class ManagedClass
+{
+ public int Number { get; set; }
+}

src/WinRT.Runtime/IWinRTObject.net5.cs

@@ -159,6 +159,13 @@ internal sealed bool IsInterfaceImplementedFallback(RuntimeTypeHandle interfaceT
  }
  }
 
+ // Make sure we are going to do a QI on a WinRT interface,
+ // otherwise we can get a helper type for a non WinRT type.
+ if (!Projections.IsTypeWindowsRuntimeType(type))
+ {
+ return false;
+ }
+
  Type helperType = type.FindHelperType();
  if (helperType is null || !helperType.IsInterface)
  {