Merged lp:~widelands-dev/widelands/bug-1805508-burning-military-sites:
When a medium military building is conquered, small military buildings very close to it burn down without a fight. When multiple small military buildings are burned down at once, the game crashes due to a failed assertion (when releasing the area of the small sites) when the areas to conquer overlap, and part of it has already been conquered. Removed this assertion.