Allow shooting npcs

[BevapDin]

• Make game::npc_at return the npc object directly (not the index in game::active_npc)
• Add game::critter_at to get any kind of critter, be it a monster, a npc or the player, this should make many things easier, instead of

if(there a monster) {
    do something
} else if(there is a npc) {
    do something
} else if(there is the player) {
    do something
}

one can write

Creature *critter = critter_at();
if(critter != NULL) {
    do something
}

The function is currently only used in the projectile attack code, because the other code uses different functions for npc and monsters, those have not been ported to Creature.

Bug report here http://smf.cataclysmdda.com/index.php?topic=5324 should be fixed by this.

Fixes #6026

Superseded by #6091

[Rivet-the-Zombie]

While this certainly allows us to target and shoot at NPCs, it also causes the game to immedately crash whenever the bullet actually hits them.

[BevapDin]

I can't reproduce this, tried it with several npcs at once, some hostile, some not. How did you trigger that crash?

[Rivet-the-Zombie]

It happens almost every time I shoot an NPC and hit.

Program received signal SIGSEGV, Segmentation fault. Segmentation fault 0xfeeefeee in ?? ()

Windows 7 console, by the way.

[BevapDin]

Turns out I had forgotten to change some calls to npc_at to the new return type, but that should only affect the tiles build and should result in a compile error.

Seems I have to get hands on a windows machine.