fix potential dupe glitch with stackable fluid containers

happens on fabric in https://github.com/Fabricators-of-Create/Create/issues/296

src/main/java/com/simibubi/create/content/contraptions/fluids/actors/ItemDrainTileEntity.java

@@ -76,6 +76,7 @@ public class ItemDrainTileEntity extends SmartTileEntity implements IHaveGoggleI
 			return returned;
 
 		transportedStack = transportedStack.copy();
+		transportedStack.stack = inserted.copy();
 		transportedStack.beltPosition = side.getAxis()
 			.isVertical() ? .5f : 0;
 		transportedStack.prevSideOffset = transportedStack.sideOffset;