Fixed a few issues with drones moving through portals.

For one, they won't also drop themselves as items anymore.
For two, they won't shut down after moving through the portal anymore.
Also corrected the target position relocation.

src/main/scala/li/cil/oc/common/entity/Drone.scala

@@ -334,23 +334,6 @@ class Drone(val world: World) extends Entity(world) with MachineHost with intern
     }
   }
 
-  override def setDead() {
-    super.setDead()
-    if (!world.isRemote) {
-      machine.stop()
-      machine.node.remove()
-      components.disconnectComponents()
-      components.saveComponents()
-      val stack = api.Items.get(Constants.ItemName.Drone).createItemStack(1)
-      info.storedEnergy = control.node.localBuffer.toInt
-      info.save(stack)
-      val entity = new EntityItem(world, posX, posY, posZ, stack)
-      entity.delayBeforeCanPickup = 15
-      world.spawnEntityInWorld(entity)
-      InventoryUtils.dropAllSlots(BlockPosition(this: Entity), mainInventory)
-    }
-  }
-
   override def onUpdate() {
     super.onUpdate()
 
@@ -488,15 +471,63 @@ class Drone(val world: World) extends Entity(world) with MachineHost with intern
 
   // ----------------------------------------------------------------------- //
 
+  private var isChangingDimension = false
+
   override def travelToDimension(dimension: Int) {
-    // Store relative target and update after teleportation, because our frame
-    // of reference most certainly changed (i.e. we'll spawn at different
-    // coordinates than the ones we started traveling from).
-    val relativeTarget = Vec3.createVectorHelper(targetX - posX, targetY - posY, targetZ - posZ)
-    super.travelToDimension(dimension)
-    targetX = (posX + relativeTarget.xCoord).toFloat
-    targetY = (posY + relativeTarget.yCoord).toFloat
-    targetZ = (posZ + relativeTarget.zCoord).toFloat
+    // Store relative target as target, to allow adding that in our "new self"
+    // (entities get re-created after changing dimension).
+    targetX = (targetX - posX).toFloat
+    targetY = (targetY - posY).toFloat
+    targetZ = (targetZ - posZ).toFloat
+    try {
+      isChangingDimension = true
+      super.travelToDimension(dimension)
+    }
+    finally {
+      isChangingDimension = false
+      setDead() // Again, to actually close old machine state after copying it.
+    }
+  }
+
+  override def copyDataFrom(entity: Entity, unused: Boolean): Unit = {
+    super.copyDataFrom(entity, unused)
+    // Compute relative target based on old position and update, because our
+    // frame of reference most certainly changed (i.e. we'll spawn at different
+    // coordinates than the ones we started traveling from, e.g. when porting
+    // to the nether it'll be oldpos / 8).
+    entity match {
+      case drone: Drone =>
+        targetX = (posX + drone.targetX).toFloat
+        targetY = (posY + drone.targetY).toFloat
+        targetZ = (posZ + drone.targetZ).toFloat
+      case _ =>
+        targetX = posX.toFloat
+        targetY = posY.toFloat
+        targetZ = posZ.toFloat
+    }
+  }
+
+  override def setDead() {
+    super.setDead()
+    if (!world.isRemote && !isChangingDimension) {
+      machine.stop()
+      machine.node.remove()
+      components.disconnectComponents()
+      components.saveComponents()
+    }
+  }
+
+  override def kill(): Unit = {
+    super.kill()
+    if (!world.isRemote) {
+      val stack = api.Items.get(Constants.ItemName.Drone).createItemStack(1)
+      info.storedEnergy = control.node.localBuffer.toInt
+      info.save(stack)
+      val entity = new EntityItem(world, posX, posY, posZ, stack)
+      entity.delayBeforeCanPickup = 15
+      world.spawnEntityInWorld(entity)
+      InventoryUtils.dropAllSlots(BlockPosition(this: Entity), mainInventory)
+    }
   }
 
   override def getCommandSenderName = Localization.localizeImmediately("entity.oc.Drone.name")