title: Updating selection of server-side selectize input with >1000 choices fails
body: <p>I have a shiny app containing a server-side selectize input with a long list (>10k) of choices.
  I would like to update the selection upon clicking a button. Here is a reproducible example</p>
  
  <pre><code>library(shiny)
  
  ui &lt;- fluidPage(
    actionButton('buttonid','Button'),
  
    selectizeInput("listid", "A long list", choices = NULL)
    )
  
  server &lt;- function(input, output, session) 
    {
    updateSelectizeInput(session, "listid", choices = paste("Item", 1:10000), server = T)
    observeEvent(input$buttonid,
                 {
                 updateSelectizeInput(session, "listid", selected = "Item 1234")
                 })
    }
  
  shinyApp(ui = ui, server = server)
  </code></pre>
  
  <p>The above code results in a blank selection when I press the button.
  However, if I search for "Item 1234", then change selection, and press the button, now the item gets selected.</p>
  
  <p>Also, trying to select an item between Item 1 and 1000 does not give problems, presumably because 1000 items get loaded at the beginning.</p>
  
  <p>This seems akin to this old bug, but I am not sure if there is a workaround <a href="https://github.com/rstudio/shiny/issues/1018" rel="nofollow noreferrer">https://github.com/rstudio/shiny/issues/1018</a></p>