Fixed issue which created large empty areas on two-level maps.

lib/rmg/CRmgTemplateZone.cpp

@@ -387,6 +387,8 @@ void CRmgTemplateZone::initFreeTiles (CMapGenerator* gen)
 	{
 		return gen->isPossible(tile);
 	});
+	if (freePaths.empty())
+		freePaths.insert(pos); //zone must have at least one free tile where other paths go - for instance in the center
 }
 
 void CRmgTemplateZone::createBorder(CMapGenerator* gen)