Unknown land / nomad map has unfair mountain

[elexis]

In one of the maps generated by unknown land / unknown nomad map script, there is a central mountain that divide all players with only a small passage between neighboring players.

This mountain is accessible to exactly one player. Thus his team can easily go onto that mountain and deny the enemy trade. As the other team can't reach that mountain, this must be fixed.

[elexis]

It's the "Passes" variant of the Unknown maps. The issue can be observed vey well with the pathfinder grid in atlas (#4842).

(In this variant there is a small disk shaped area in the middle, acting as a filler for any part of the central area that wasn't filled by the mountainrange. So first thought was to increase the size, but the bug still occurs when increasing the radius by a factor of 3.)

The issue occurs exactly when the waveforms of two neighboring mountains coincidentally result in them being nearly parallel. Only then the mountains become reachable after the smoothing of the elevation with neighboring tiles.

Reducing the smoothing from 3 to 1 solves the issue described in this report, (but not the nomad mountain bug reported in #3140)

[elexis]

In 20434:

Prevent the mountains on the Unknown map variant "Passes" from becoming passable to only one player. Fixes #4060.