Allow cancelling an activity without aborting the entire queue

OpenRA.Mods.Common/Activities/PickupUnit.cs

@@ -157,12 +157,12 @@ namespace OpenRA.Mods.Common.Activities
 			});
 		}
 
-		public override bool Cancel(Actor self)
+		public override bool Cancel(Actor self, bool keepQueue = false)
 		{
 			if (!IsCanceled && innerActivity != null && !innerActivity.Cancel(self))
 				return false;
 
-			return base.Cancel(self);
+			return base.Cancel(self, keepQueue);
 		}
 	}
 }