Inifinite observe loop is possible

[bellma-lilly]

I recently fixed #34 "Callback is not received by server when same tree structure is sent twice"

However, this introduces a possible infinite loop because there is a callback whenever the tree is changed:
observe(
req(input$tree)
updateTree(...)
}

There are two sides to this; it makes sense to me that other parts of the code would be alerted when the tree changes with updateTree (input$tree acts as reactive). But, in the current code, the user would need to check for changes in the tree to avoid an infinite loop:
observe(
req(input$tree)
if(input$tree != lastTree){
updateTree(...)
lastTree <- input$tree
}
}

thoughts?