avm2: Remove last use of coerce_to_object outside of core code

Author: Lord-McSweeney

core/src/avm2/globals/flash/display/display_object.rs

@@ -768,7 +768,15 @@ pub fn set_transform<'gc>(
     // FIXME - consider 3D matrix and pixel bounds
     let matrix = transform
         .get_public_property("matrix", activation)?
-        .coerce_to_object(activation)?;
+        .as_object();
+
+    let Some(matrix) = matrix else {
+        // FP seems to not do anything when setting to a Transform with a null matrix,
+        // but we don't actually support setting the matrix to null anyway
+        // (see the comment in `flash::geom::transform::set_matrix`)
+        return Ok(Value::Undefined);
+    };
+
     let color_transform = transform
         .get_public_property("colorTransform", activation)?
         .as_object()

core/src/avm2/globals/flash/geom/transform.rs

@@ -80,6 +80,9 @@ pub fn set_matrix<'gc>(
     this: Object<'gc>,
     args: &[Value<'gc>],
 ) -> Result<Value<'gc>, Error<'gc>> {
+    // TODO: Despite what the docs say, FP accepts a null matrix here, and returns
+    // null when trying to get the matrix- but the DO's actual transform matrix will
+    // remain its previous non-null value.
     let matrix = object_to_matrix(args.get_object(activation, 0, "value")?, activation)?;
     let dobj = get_display_object(this, activation)?;
     dobj.set_matrix(activation.context.gc_context, matrix);