[ok] Additional tech stops distance calculated incorrectly

[tyteen4a03]

Steps to reproduce:

1. Create a route from OMDB to RJTT.
2. Add OPRN as a tech stop. The distance between OMDB-OPRN is shown.
3. Add ZBTJ as a tech stop. The distance between OMDB-ZBTJ is shown, instead of OPRN-ZBTJ.