Corner case when having 0 trains/stations again

[andersoyvind]

From the moment an LTN station is placed, the LTN Manager dialog is available.

Actual: If all stations are removed, the dialog shows Station (1) still.

Expected: When removing the last station, the LTN Manager is disabled again, or the number of stations in the tab is changed to 0.

Reproduce:

Place track Place LTN station Open LTN Manager - verify that 1 station exists Remove LTN station Notice that Manager is not updated, previous state is stale.