tests: Fix addressing of buffers in tests
tests: Fix addressing of buffers in tests

They were being referenced once too much, which was causing the tests to
write into arbitrary memory.

Coverity CID: 249795

Signed-off-by: Philip Withnall <withnall@endlessm.com>

https://bugzilla.gnome.org/show_bug.cgi?id=792402

GNOME/glib-networking,GNOME/glib-networking,GNOME/glib-networking