Do not perform transfer processing for child requests to related stations

This fixes transfer trains getting lost when requested from a related station

Notable offender: "Berlin Südkreuz" lacked S 41 / S42 (ring line
from Südkreuz (S) to Südkreuz (S) with transfer to/from the next/previous
incarnation), as it referenced "Berlin Südkreuz (S)". "Berlin Südkreuz (S)"
itself worked fine.