Bread is basically just flour, water, and yeast, so it's pretty hard to make it inedible unless you burn it to a crisp in the oven.
The difference between all-purpose flour and bread flour is gluten strength; if you substitute all-purpose flour then your bread won't rise as high or be as strong; this is a desirable quality in, say, cake, but not bread.
However, AP flour isn't that far off from bread flour in terms of gluten; while cake flour may be as low as 6% and bread flour can be as high as 14%, AP flour tends to weigh in at around 10% or more, which is why it's called "all-purpose". As Michael says, yeast bread is actually not as sensitive to the exact quantities as (for example) most pastries, but it's still better to use a recipe that was actually built around AP flour instead of just trying to substitute it for bread flour.
If you are determined to make the substitution, then I would suggest you try to find some wheat gluten and add a small amount of that to the AP flour. Mathematically, if you assume that you're lacking some 3% protein, then you'd want to add about 1 tbsp of gluten for every 2 cups of flour. It's really not much, though, and if you don't have or can't find wheat gluten then your bread would probably survive anyway with AP flour, it just might be a little denser than you expect.
The author of this recipe probably happens to keep in his pantry (or more professionally speaking, dry store) just those two types of flour, and so has specified a mix to get a mid-level flour with moderate protein levels, tailored to his preferences. Given that the author is Jacques Torres, this is almost certainly a scaled down translation of a professional recipe, where that is not an uncommon practice (the very odd measurements support the idea of scaling and rounding; the weird flour measurements are probably the closest volume equivalent to a weight based scaled recipe).
Two commercial varieties (all purpose, and the less common pastry flour) also have protein levels in between cake flour and bread flour, with pastry flour being somewhere between cake flour and all purpose, typically.
If you happen to have all purpose (and you almost certainly do) I would suggest using it in the recipe for the total of both specialty flours. Very few cookie recipes are so fussy that it will actually matter very much.
Best Answer
What you really need is "in the middle". Shortbread cookies are not very different from shortbread pie crust, they use the same principle, but a different shape. So the optimal flour would be pastry flour, at 6-7% gluten, which is between cake flour (4-5%) and AP (7-8%).
If you are not aiming for five-star-perfection according to century-old traditional tastes, either of your flours will do well. AP is probably a bit safer, in the sense that the cookies won't fall apart too easily.