Fixed "divided by zero" error when returning 0 in AMMOCOST hook

* with CheckWeaponAmmoCost=1

Added a value check to the return value of AMMOCOST hook.
Updated hookscripts.md to reflect this change.

artifacts/scripting/hooks.yml

@@ -296,9 +296,11 @@
   id: HOOK_AMMOCOST
   doc: |
     Runs when calculating ammo cost for a weapon. Doesn't affect damage, only how much ammo is spent.<br>
-    By default, weapons can make attacks when at least 1 ammo is left, regardless of ammo cost calculations.<br>
+    By default, a weapon can perform an attack with at least one ammo, regardless of ammo cost calculation.<br>
     To add proper check for ammo before attacking and proper calculation of the number of burst rounds (hook type 1 and 2 in `arg3`), set **CheckWeaponAmmoCost=1** in **Misc** section of ddraw.ini.
 
+    __NOTE:__ The return value must be greater than or equal to 0 to be valid.
+
     ```
     Item    arg0 - The weapon
     int     arg1 - Number of bullets in burst or 1 for single shots

artifacts/scripting/hookscripts.md

@@ -394,9 +394,11 @@ int     ret1 - The new maximum damage
 #### `HOOK_AMMOCOST (hs_ammocost.int)`
 
 Runs when calculating ammo cost for a weapon. Doesn't affect damage, only how much ammo is spent.\
-By default, weapons can make attacks when at least 1 ammo is left, regardless of ammo cost calculations.\
+By default, a weapon can perform an attack with at least one ammo, regardless of ammo cost calculation.\
 To add proper check for ammo before attacking and proper calculation of the number of burst rounds (hook type 1 and 2 in `arg3`), set **CheckWeaponAmmoCost=1** in **Misc** section of ddraw.ini.
 
+__NOTE:__ The return value must be greater than or equal to 0 to be valid.
+
 ```
 Item    arg0 - The weapon
 int     arg1 - Number of bullets in burst or 1 for single shots