[12640] Better value to check distance between owner and pet. This problem was introduced in [12565] https://github.com/cmangos/mangos-wotlk/commit/897ed8271d4c1ae35a3703e48bbf9c418bb4bf4f

Maybe i misunderstaind that commit but the pet now follow correctly its master.
Before the minimal check distance was too small so pet position was updated every update.

Fix cmangos/issues#269