Taking into account #4 it seems that the game itself already takes care of not allowing the 0 value. If it does, it seems like 0 is not an acceptable value.
Excuse me if I am wrong but I would compare it to the CS 1.6 cl_bob* cvars and with regard to them any other values different from default was not allowed.
I know this aint the place to ask my question but can any1 of u help me with fps of CSGO, i get only 40 fps while my specs are well above the minimum required. =/
Try to clean your PC from dust. Not sure, but it might be useful. Also try to disable Vsync in game options, and in VGA settings. And try to run game in window mode.
I had problem with dust in the past, after 5-10 minutes of play, my fps was dropped to 15 instead of 100-150 in every game. My VGA burns like hell, because cooler did worked poorly due to dust. My English is bad, but i hope you are understand me.