avm1: Pass undefined this for CallMethod with non-string method_name

This isn't the most accurate behavior, since it should be an unboxed
Value, but currently it's not possible due to #843.

core/src/avm1/activation.rs

@@ -860,8 +860,9 @@ impl<'a, 'gc, 'gc_context> Activation<'a, 'gc, 'gc_context> {
             // Call `this[method_name]`
             object.call_method(&method_name.as_str(), &args, self)?
         } else {
-            // Undefined/empty method name; call `this` as a function
-            let this = self.target_clip_or_root()?.object().coerce_to_object(self);
+            // Undefined/empty method name; call `this` as a function.
+            // TODO: Pass primitive value instead of boxing (#843).
+            let this = Value::Undefined.coerce_to_object(self);
             object.call("[Anonymous]", self, this, None, &args)?
         };
 

core/src/avm1/timer.rs

@@ -50,7 +50,7 @@ impl<'gc> Timers<'gc> {
         );
 
         // TODO: `this` is undefined for non-method timer callbacks, but our VM
-        // currently doesn't allow `this` to be a Value.
+        // currently doesn't allow `this` to be a Value (#843).
         let undefined = Value::Undefined.coerce_to_object(&mut activation);
 
         let mut tick_count = 0;