Prevent character from being Dead on Arrival.

[kevingranade]

Summary

SUMMARY: None

Purpose of change

In #36470 a fix to avoid undefined behavior resulted in leaving characters in a bad state upon character creation, namely their max HP was pinned to 0.

Describe the solution

Instead of skipping the code where undefined behavior was occurring (seriously, this is never a good idea!), add code to insure that the desired semantics are preserved even when max_hp for a body part happens to be 0.
Also initialized max_hp for all body parts to 1 instead of 0, and patched another location where max_hp was potentially 0 to instead floor it at 1.

Testing

The NPC behavior test no longer crashes.
You can now spawn a character without them immediately dying.

Additional context

Since this is one of the few classes of bugs that makes the game literally unplayable, I'm going to merge this once the test suite completes.

Hope this is the last time
'cus we never should've merged this code
This character has been, dead. on. arrival.
And there's no way to play this game
This character has been, dead. on..

A rivalry goes so deep between me
And this loss of sleep over bugs

This is patch one
Merge it real fast
I know this ain't your favorite bugfix
The games you grow to like, never stick at first
So I'm writing you a bugfix
And here's a release

No, it's not the last time
'cus we'd never close your PR
This character is still, dead. on. arrival.
And there's no way to play this game
This character has been, dead. on..

A rivalry goes so deep between me
And this loss of sleep over bugs

This is patch one
Merge it real fast
I know this ain't your favorite bugfix
The games you grow to like, never stick at first
So I'm writing you a bugfix
And here's a release

This is patch one
Merge it real fast
I know this ain't your favorite bugfix
So-o-o-o

This is patch one
Merge it real fast
This is patch one
Merge it real fast
I know this ain't your favorite bugfix
The games you grow to like, never stick at first
So I'm writing you a bugfix
And here is your...

[ZhilkinSerg]

Fixes #36487

[kevingranade]

This pull request has been mentioned on Cataclysm: Dark Days Ahead. There might be relevant details there:

https://discourse.cataclysmdda.org/t/instant-death-on-generation/22314/3

[hexagonrecursion]

I have learned my lesson: compiling C++ is SLOW, but the alternative is INFINITELY WORSE. Also: cool poem.