Bug report #330  -  Preview Window case a Synfig Studio crash

I have disabled Preview Window (sensitive = false) through the "dialog-flipbook" action (yes it's the call the preview window :) until the Preview Option is called (and the preview window is created.)
Then, the action is always enabled (the preview window is only hided on close_event, never is closed)

Possible improvement, let Preview Window action be always sensitive and call Preview Option the first time.