chat screen: Work around that RN bug so UnreadNotice renders too.
chat screen: Work around that RN bug so UnreadNotice renders too.

After the parent commit, the bug starts affecting UnreadNotice.
Work around that in the same way.  See #3089 for detailed debugging.

vishwesh3/zulip-mobile,vishwesh3/zulip-mobile,vishwesh3/zulip-mobile,vishwesh3/zulip-mobile