Fixed aircraft in TS landing instantly to reload their ammo

- Updated calculating the landing altitude for the Land activity not taking into account the terrain height.
- Fixes 14312.

OpenRA.Mods.Common/Activities/Air/Land.cs

@@ -44,7 +44,8 @@ namespace OpenRA.Mods.Common.Activities
 				return NextActivity;
 			}
 
-			Fly.FlyToward(self, plane, d.Yaw.Facing, new WDist(target.CenterPosition.Z));
+			var landingAlt = self.World.Map.DistanceAboveTerrain(target.CenterPosition);
+			Fly.FlyToward(self, plane, d.Yaw.Facing, landingAlt);
 
 			return this;
 		}