All standard carry models I'm familiar with either have a hard trigger pull, or have a manual safety. I'll grant you that someone carrying the latter had better have it in a holster or some arrangement where the safety can't get pushed off ... but then again, if this is how they normally carry, e.g. a normal purse, if they don't do that they're always in danger of a negligent discharge. And there are modified guns out there with unreasonably light trigger pulls, but the same considerations above for protecting a manual safety hold.

So I'd say "very low", while agreeing that it's not zero.

BTW, it's almost never an accidental discharge, almost always a negligent one, and in this hypothetical case most certainly so.