The "Edit function" isn't disabled after deselecting it.
Steps to reproduce:
* have a curve plot and a function on a graph
* go there in the "Add/Remove Curve" dialog
* select the function
* select the table data
* click on "Edit function"
=> segmentation fault.
Patch #3106338 (minus a little buglet).
From: Dominik K. <dominik_k@...>
