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/ddraw.ini

@@ -619,7 +619,7 @@ ExplosionsEmitLight=0
 ;MovieTimer_artimer4=360
 
 ;Set to 1 to add proper check for ammo before attacking and proper calculation of the number of burst rounds
-;By default, weapons can make attacks when at least one 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
 ;Note that enabling this option will prevent super cattle prods and mega power fists from attacking with only one ammo left
 CheckWeaponAmmoCost=0
 

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

sfall/Modules/Combat.cpp

@@ -110,7 +110,7 @@ long __fastcall Combat::check_item_ammo_cost(fo::GameObject* weapon, fo::AttackT
 	}
 
 	// calculate the cost
-	long cost = (newRounds != rounds) ? newRounds / rounds : 1; // 1 - default cost
+	long cost = (newRounds != rounds) ? (newRounds / rounds) : 1; // 1 - default cost
 	return (cost > currAmmo) ? 0 : currAmmo; // 0 - this will force "Not Enough Ammo"
 }
 
@@ -171,6 +171,7 @@ static long __fastcall divide_burst_rounds_by_ammo_cost(long currAmmo, fo::GameO
 		roundsCost = burstRounds;                   // rounds in burst (the number of rounds fired in the burst)
 		AmmoCostHook_Script(2, weapon, roundsCost); // roundsCost returns the new cost
 	}
+	if (roundsCost == 0) return burstRounds;        // cost is free, skip the rest of calculation
 
 	long cost = burstRounds * roundsCost; // amount of ammo required for this burst (multiplied by 1 or by the value returned from HOOK_AMMOCOST)
 	if (cost > currAmmo) cost = currAmmo; // if cost ammo more than current ammo, set it to current

sfall/Modules/HookScripts/CombatHs.cpp

@@ -350,7 +350,7 @@ int __fastcall AmmoCostHook_Script(DWORD hookType, fo::GameObject* weapon, DWORD
 
 	RunHookScript(HOOK_AMMOCOST);
 
-	if (cRet > 0) rounds = rets[0]; // override rounds
+	if (cRet > 0 && (long)rets[0] >= 0) rounds = rets[0]; // override rounds
 
 failed:
 	EndHook();