fix "Explosion processing is delayed to end of turn for explode-on-impact ammo"

[leoCottret]

Summary

SUMMARY: Bugfixes "add explosion effect triggers after each explosive ammo is shot"

Purpose of change

Fixes #1904

Describe the solution

Adding a "explosion_handler::get_explosion_queue().execute();" after a projectile is shot.
(Cf additional context of the issue for more details)
I repeated the steps in the issue, shotted 5 ammoes and got 5 nice explosions, precisely one after each shot,

Describe alternatives you've considered

None for now

Testing

I repeated the steps in the issue.
I also tried some grenades but they worked fine. And I think it's not even related.
I tried to do the same by giving a weapon to a NPC, and I think it works, but he one shotted himself with it. Is it me or they don't seem to be able to shoot at more than 3 meters even with the right commands?

Additional context

About this part
"This may require some measure to prevent two executes being called on the same queue in one call stack."
I suppose we're safe, unless I'm missing something, because the explosion queue uses a singleton (the explosion queue will always be the same object), so even if it's called several times at different places in one turn, the object will always be updated between each call.

[Coolthulhu]

I was worried about chain explosions, but I can't find a good way of causing those.
If they can happen, we'll need a special case for them. For example, having explosion queue operate on a temporary. Otherwise it might run into an undefined behavior as the queue it is processing changes mid-processing.