Event "plotly_legendclick" returns unreasonable results for member $visible

Brief description of the problem:

1. For a first click on a(ny) legend entry there is no member $visible at all, even though the markers are not visible.
2. For even numbers of clicks on legend entries $visible is "legendonly" (markers are shown).
3. For odd numbers of clicks $visible is TRUE (respective markers are not shown).

Please consider as reprex:
https://github.com/ropensci/plotly/blob/master/inst/examples/shiny/event_data_legends/app.R

使用 inst/examples/shiny/event_data_legends/app.R 重现三个图例点击案例，记录每次点击后的事件 payload 和 $visible 行为。从该示例开始追踪事件数据处理；完成标准是第一次点击包含 $visible，且后续值准确反映标记是否可见。