I've seen this mentioned elsewhere.
This is equivalent to the AI assigning getting killed a zero probability.
One problem is that the AI might decide to give everyone a button to kill it, so that they feel better about the AI. It will assume that nobody will press the button (or not care if they do), but someone is bound to.
Make it indifferent to a specific person or group blowing it up, not to anyone doing so.
I just noticed that LessWrong has not yet linked to FHI researcher Stuart Amstrong's brief technical report, Utility Indifference (2010). It opens: