[faff]

Ehhh... Use "1 ammo" as 0 ammo.

PHP код:

public OnPlayerWeaponShot(playerid, weaponid, hittype, hitid, Float:fX, Float:fY, Float:fZ)
{
   new ammo = GetPlayerAmmo(playerid); // Getting player his current ammo.
   new weapon = GetPlayerWeapon(playerid); // Getting player his current weapon.
   if(ammo == 1){ // Check if player has 1 ammo.
   SetPlayerAmmo(playerid, weapon, 1); // Prevent the weapon from dissappearing.
   return 0;} // Bullet won't do damage. 
   else{
   return 1;}
} 


Tested it and works perfect.
It won't shoot any bullet when having 1 ammo.
REMINDER: Since a minigun and someother weapons are shooting to fast you'll have to raise the amount of ammo for these. Tested this with Desert Deagle, Colt45, Shotgun, Spaz-12 and Grenades and was working perfectly.
It didn't work with Miniguns since it was shooting to fast. Just raise up if(ammo == 1) to if(ammo == 2).