Fix armaments/projectiles to aim at closest Target.Positions

Instead of CenterPosition.
TargetablePositions were already used for targeting/attack decisions, but not armaments/projectiles.

OpenRA.Mods.Common/Traits/Armament.cs

@@ -229,7 +229,7 @@ namespace OpenRA.Mods.Common.Traits
 				Source = muzzlePosition(),
 				CurrentSource = muzzlePosition,
 				SourceActor = self,
-				PassiveTarget = target.CenterPosition,
+				PassiveTarget = target.Positions.PositionClosestTo(muzzlePosition()),
 				GuidedTarget = target
 			};