fix: add safety checks to prevent runtime crashes

Scripts/ConveyerController.gd

@@ -4,19 +4,19 @@ var selected
 var events = []
 var destination = []
 var conveyer = []
-var conveyerInd=0
+var conveyerInd = 0
 var dragging
 var sendingEnd = false
 var can_send = false
 var started = false
 
 func initialise():
-	self.selected
+	self.selected = null
 	self.events = []
 	self.destination = []
 	self.conveyer = []
 	self.conveyerInd = 0
-	self.dragging
+	self.dragging = null
 	self.sendingEnd = false
 	self.can_send = false
 	self.started = false
@@ -32,26 +32,53 @@ func setup(conveyer) -> void:
 func _ready() -> void:
 	pass # Replace with function body.
 
-
 # Called every frame. 'delta' is the elapsed time since the previous frame.
 func _process(delta: float) -> void:
 	if self.can_send and not self.started and self.destination != null:
 		self.send_event()
 	pass
 
 func create_conveyor():
+	# SAFETY: prevent crash due to invalid access
+	if selected == null:
+		return
+	if conveyerInd >= conveyer.size():
+		return
+	if destination == null or conveyerInd >= destination.size():
+		return
+
 	conveyer[conveyerInd].set_point_position(0, selected.get_position())
 	conveyer[conveyerInd].set_point_position(1, destination[conveyerInd])
-	conveyerInd+=1
-	
+	conveyerInd += 1
+
 func send_event():
 	print("sending events!")
 	self.started = true
-	if conveyerInd!=0:
-		for n in events.size():
-			events[n].sending = true
-			var tween = get_tree().create_tween()
-			tween.tween_property(events[n], "position", destination[n%conveyerInd], 2).set_trans(tween.TRANS_LINEAR)
-			if n%conveyerInd==conveyerInd-1:
-				await tween.finished
+
+	# SAFETY: avoid divide by zero or empty destination
+	if conveyerInd == 0:
+		return
+	if destination == null or destination.size() == 0:
+		return
+
+	for n in events.size():
+		# SAFETY: ensure event still exists before accessing it
+		if not is_instance_valid(events[n]):
+			continue
+
+		events[n].sending = true
+		var tween = get_tree().create_tween()
+
+		var dest_index = n % conveyerInd
+		if dest_index < destination.size():
+			tween.tween_property(
+				events[n],
+				"position",
+				destination[dest_index],
+				2
+			).set_trans(tween.TRANS_LINEAR)
+
+		if dest_index == conveyerInd - 1:
+			await tween.finished
+
 	Level.next_level()