Reset ammo count at the start of tactical and improve HotLoadedAmmo's code

[Styrium]

Resolves #1624

[Tedster59]

@Styrium does this cause issues for items that don't have ammo or clip size, such as non-weapons?

[Styrium]

Well, for items that aren't X2WeaponTemplate or X2AmmoTemplate that value gets set to -1, which is the same value it gets on creation for those items. I think nothing has altered that value at this point in the pipeline. Effects that grant extra uses of abilities should trigger afterwards.

However, it will overwrite the MergeAmmoAsNeeded() behavior, so there needs to be an extra check before calling it.

[Styrium]

I'm fairly certain it should be safe to merge now