I believe the salient point is that there isn't ammo "placed into a position from which it can be fired" if you have an empty magazine inserted into the magazine well.
However, make sure your full magazine is plainly visible. This is accomplished usually in a magazine carrier/pouch on your belt, just like your pistol. THIS IS IMPORTANT! A magazine is an integral part of a pistol. Carrying it with ammo in it in your pocket could potentially bring a concealed weapons violation (p.c. 12025).
If you are carrying a revolver you may carry speed loaders, bullets, etc. in your pocket without concern, 'cuz a speed loaded or moon clips are not an integral part of a revolver.