cleanup: Don't assume hasOwnProperty() method on objects

cleanup: Don't assume hasOwnProperty() method on objects

Since ES5, it is possible to create objects with no prototype at all:

    let foo = Object.create(null);

Those object won't have any builtin properties like hasOwnProperty(),
which is why eslint added a corresponding rule to its default rule set.

While this isn't an issue that affects our code, there's no harm in fol-
lowing the recommendation and call the method through Object.prototype.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/716