Fix uninitialized monster::horde_attraction

[hexagonrecursion]

Summary

SUMMARY: Bugfixes "Fix uninitialized monster::horde_attraction"

Purpose of change

Fixes #36813 - code to initialize monster::horde_attraction was missing.

Describe the solution

Added code to the constructor to initialize the field. I used the same default value as the json loading code

Cataclysm-DDA/src/savegame_json.cpp

Line 1901 in 6674292

horde_attraction = static_cast<monster_horde_attraction>( data.get_int( "horde_attraction", 0 ) );

Note: initial value of MHA_NULL will result in horde_attraction being randomized by monster::get_horde_attraction.

Cataclysm-DDA/src/monster.cpp

Lines 2839 to 2845 in 605409a

	monster_horde_attraction monster::get_horde_attraction()
	{
	if( horde_attraction == MHA_NULL ) {
	horde_attraction = static_cast<monster_horde_attraction>( rng( 1, 5 ) );
	}
	return horde_attraction;
	}

Describe alternatives you've considered

Testing

Additional context

[hexagonrecursion]

I accidentally submitted PR before filling the description. I then ninja-edited it, but PR Validator did not run again.

[anothersimulacrum]

It did, it just didn't remove the failed run.