I'll echo Hobbes on this one. It's unlikely to come up a lot, and if it does, I personally don't see any good reason to invent a rule preventing an attack that will pretty much auto award your target Edge (I would imagine their DR is at least 4).
Edit: I want to elaborate a little. Whatever happened to just playing a game using the rules of the game? If that SA/BF/FA firing at penalty makes attacking with insert weapon here an AR of 0, so you determine that should not be possible and they have to switch to insert other weapon here that likely has very little mechanical difference in stats (maybe 1 DV) but substantially better AR because it is above 0, what is really the difference there that we need to invent rules to prevent it?
For example, I want to shoot my Ares Alpha in BF mode at max range so I can score a 6DV hit. My GM decides I can't, because they don't like the idea of me being able to use a weapon with AR 0. I switch to my Remington 900, fire that in SA mode, for a 6DV hit with AR 12.
Is that really worth making up rules over? Weapons in this edition are nearly identical mechanically, so what is the value of that hassle and annoyance to the player?