Assertion failed when making a port at top left position in this safegame

[SirVer]

When placing a port in this safegame the following assertion fails:

[Host]: Requesting sync reports for time 5855513
[Host]: Client 0: Time 5854940
[Host]: Client 0: Time 5855513
[Host]: comparing syncreports for time 5855513
Forcing flag at (114, 17)
Assertion failed: (f.field->immovable->get_size() == NONE), function set_position, file /Users/sirver/Desktop/Programming/cpp/widelands/bzr_repo/src/logic/immovable.cc, line 76.

to reproduce: load the game, speed up till the blue ship finds a port space (it is on an expedition), then order a port to be placed there.

[Nasenbaer (nasenbaer)]

Seems the assert was a leftover from the times where there were no force_building or force_csite functions. Quite a wonder that this assert has never been triggered before.
assert removed and comment added in bzr rev. 6736

[SirVer (sirver)]

Released in build-18 rc1.