Take bath towels and use them to wrap the corners of the one side of your ladder – the side that will come in contact with the glass window. To strengthen the grip of towels, wrap them tightly using duct tape.
You can then properly check the wrapped area and see if there is any pointed or hard edge left. In essence, you are trying to create a greater space which will make contact with the window and are also trying to minimize the impact of the hard word on the glass. Rather than two ends of the ladder making contact, you are distributing the weight with the towel. If the two points are still prominent then you will need more towels until it feels like one solid mass.
Rest the ladder against any wood trim that is on the glass window. Many windows have panes surrounded by little pieces of wood. If your windows look like this, rest the newly created towel surface on the wood instead of the window. This will give you an extra layer of protection so you do not break the glass.
If you do not have rough towels, then you can also consider using any foam material, which can extend the surface of the top of the ladder, while making it softer.