tubes: don't use an uninitialized tube_id.
tubes: don't use an uninitialized tube_id.

gcc rightly points out that tube_id may be uninitialized if
extract_tube_information() returns false.

freedesktop-unofficial-mirror/telepathy__telepathy-salut,freedesktop-unofficial-mirror/telepathy__telepathy-salut,freedesktop-unofficial-mirror/telepathy__telepathy-salut,freedesktop-unofficial-mirror/telepathy__telepathy-salut