Crash when enchanting last projectiles

When you click to finalise the enchant of a projectile (for example with an enchanter service), it will crash if you have no same projectile left. Example:

("projectiles enchant multiplier" default value (0) => you can only enchant one projectile)

• You have 2+ steel arrows => it will not crash because there will be 1+ non-enchanted steel arrows left after the process.
• You have only 1 steel arrow: it will crash

("projectiles enchant multiplier" > 0 => you can enchant several projectiles)

• If soul gem charge * projectiles enchant multiplier >= enchantment strength * number of this projectile in your inventory, then it will crash

Tested with the enchanter service in Balmora Mages Guild.

with Arch Linux and Debian, with 0d25656d (march 3) and 36ff5d35 (june 6), with or without mods, with or without blank settings.cfg

The openmw.log: openmw.projectile_enchant.log

The crash log: openmw-crash.log