Update: Added protection against re-queueing a client for reading body that has been queued once already

Fix: Check if we actually have source->client->con in case we want to access source->client->con->tls

This fixed a regression caused by 4828c07d.
The patch was also applied into release-2.4.4 as c5201770.
However the patch for release-2.4.4 was correct. So no regression there.