r11731 - crash convoy filter

[Andarix]

The filter for stations and convoys is linked. If I change the filter for a station, the filter for the convoys is also changed.

Stations now have the connections filter, but this is missing for convoys.

If the filter for stations is set to connections and the filter button is clicked for a convoy, Simutrans closes.

In my opinion, this linked does not make much sense.