editor: tricky dangling waypoint connections

[matthiaskrgr]

FreedroidRPG also had this problem:

In the editor:
make waypoint A
start WP connection from A
delete waypoint A
you can now connect from no waypoint (?) to another waypoint

Waypoint nr. 14. selected as origin
Origin==Target --> Connection Operation cancelled.
Waypoint nr. 14. selected as origin
Target-waypoint 0 selected
 Connection established!

I checked the mapfile and it seems like the dangling connection is actually not saved (we had this bug in FreedroidRPG a few years ago :) ) but maybe we can reset the connection-selection as soon as the origin waypoint is removed?