fixes #9256 (error with deactivating bots and dropping ammo)

Put in fix for issue #9256. Hopefully this is all that was needed. Used similar function call as standard turret, as that still dropped ammo fine.
I suspect the laser_capacitor is not a real item, just some generic pseudo ammo item (because the game requires an ammo item for guns). It is not used when the turret is deployed in `iuse::turret_laser`, that makes it suspicious. The `monster::ammo` member is also not used in `mattack::laser`, so it's never decreased and always stays at the default value.

Another thing: there is code very similar in `game::plmove` for when the character deactivates a friendly turret by walking into it. You might want to add the same code their.