Make sure selectImageInput works with NULL choices and updateImageInput

[jpmarindiaz]

When creating images with empty choices make sure updateImageInput creates the new options

See sample app

shinyinvoer/inst/examples/app-selectImageInput.R

Lines 66 to 67 in 4bce847

	updateSelectImageInput(session, inputId = "empty_then_update",
	choices = c("First" = "first", "Second" = "second"))

[ddazal]

Is it 81153de enough to close this issue? @jpmarindiaz