io/router: fix pointer positions of Enter and Leave events for nested areas

Before this change, inverse transformations of pointer positions would
stack up, leading to incorrect positions when an enter or leave event
was delivered to multiple areas.

Signed-off-by: Dominik Honnef <dominik@honnef.co>

io/router/pointer.go

@@ -779,6 +779,7 @@ func (q *pointerQueue) deliverEnterLeaveEvents(p *pointerInfo, events *handlerEv
 		e.Type = pointer.Leave
 
 		if e.Type&h.types != 0 {
+			e := e
 			e.Position = q.invTransform(h.area, e.Position)
 			events.Add(k, e)
 		}
@@ -792,6 +793,7 @@ func (q *pointerQueue) deliverEnterLeaveEvents(p *pointerInfo, events *handlerEv
 		e.Type = pointer.Enter
 
 		if e.Type&h.types != 0 {
+			e := e
 			e.Position = q.invTransform(h.area, e.Position)
 			events.Add(k, e)
 		}