`highlight()` selectize payload isn't correct when non-crosstalk traces appear before crosstalk traces

[cpsievert]

For example, this results in an empty payload, when it should be populated

p <- plot_ly() %>%
  add_lines(data = mtcars, x = ~wt, y = ~mpg) %>%
  add_markers(
    data = highlight_key(mtcars, ~cyl, "Choose cylinder"),
    x = ~wt, y = ~mpg
  ) %>%
  highlight(selectize = TRUE)

plotly_build(p)$x$selectize

NULL

Interestingly, if you remove the add_lines() trace, you get the correct result of:

$a5634ffecff7b115d858cad5b9126e93
$a5634ffecff7b115d858cad5b9126e93$items
  value label
1     6     6
2     4     4
3     8     8

$a5634ffecff7b115d858cad5b9126e93$group
[1] "Choose cylinder"