HTTP internals: do not access reply that was deleted already

... rather than crashing.

Task-number: QTBUG-32404
(cherry picked from commit 78f9f4b4970e6f4155b7cf2e88c6ac540dec47bc)

Change-Id: Ibdffcb9f57e841655998cf72d0ee8206b4987aa7
Reviewed-by: Richard J. Moore <rich@kde.org>