QmlContext::addDefaultObject does not work for custom list properties

At 2133c9c454b8a648aad2a1993b3e239ceeeca03b the minehunt demo would not work properly. This is due to QmlContext::addDefaultObject no longer properly exposing the tiles property (which it did at 3732fb8ac1ef79b47a4e8df9c37154618a1adc5e).

There is currently a workaround where tiles is explicitly exposed with QmlContext::setContextProperty, which works. Note that the other properties of the object are still exposed fine using just addDefaultObject.