If we receive an updated frame ensure we reset cur if required.

Prior to this change `cur` can be stale, meaning the frame returned for
`WaitFrame(ctxt, cdptypes.EmptyFrameID)` will be out of date, and never updated
based on incoming events.

handler.go

@@ -524,6 +524,9 @@ func (h *TargetHandler) pageEvent(ctxt context.Context, ev interface{}) {
 	case *page.EventFrameNavigated:
 		h.Lock()
 		h.frames[e.Frame.ID] = e.Frame
+		if h.cur != nil && h.cur.ID == e.Frame.ID {
+			h.cur = e.Frame
+		}
 		h.Unlock()
 		return