Stop requesting null next replies from the server
Stop requesting null next replies from the server

A recent change (47e007e08f9bedaf47cf59a63c9bd04219195d76) introduced a
regression where we failed to check whether a reply thread has a next reply.
This meant that we would end up sending `/context/undefined` requests to the
server for every reply thread on every room view.

Fixes https://github.com/vector-im/element-web/issues/17563
Regressed by https://github.com/matrix-org/matrix-react-sdk/pull/6079

matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk