jingle-content: reset idle ID in its callback
jingle-content: reset idle ID in its callback

The callback returns FALSE so the source will be invalidated.

Recent GLib now raises a critical when attempting to remove an invalid ID,
making some jingle tests failing.

freedesktop-unofficial-mirror/wocky,freedesktop-unofficial-mirror/wocky,noonien-d/wocky,freedesktop-unofficial-mirror/wocky,noonien-d/wocky,noonien-d/wocky