Land activity: fix bug which causes crash in Aircraft.AddInflunce()

Fixes #21302

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

@@ -131,6 +131,10 @@ public override bool Tick(Actor self)
 					target = Target.FromCell(self.World, newLocation.Value);
 					targetPosition = target.CenterPosition + offset;
 					landingCell = self.World.Map.CellContaining(targetPosition);
+
+					// Since the landing cell have changed, check again; if we are already at the new landing location, then abort landing
+					if ((targetPosition - pos).LengthSquared == 0)
+						return true;
 				}
 			}