Fix: properly check for item disable status against segfault

[metaq3]

Trivia

I have a teamplay server with g_gametype 3 and some items disabled through disable_<item> cvars. I noticed, that on some maps my server was randomly crashing with SIGSEGV ( I'm using native libraries ).

This is really rare bug. I found only one way to reproduce it with guaranteed result.

Reliable way to reproduce

Build native libraries and copy them into baseq3. Download map "battleforged" ( battleforged.zip ) and make a simple config, which disables a bunch of items and adds some bots:

disable.cfg

set disable_weapon_gauntlet 1
set disable_weapon_shotgun 1
set disable_weapon_machinegun 1
set disable_weapon_grenadelauncher 1
set disable_weapon_rocketlauncher 1
set disable_weapon_lightning 1
set disable_weapon_railgun 1
set disable_weapon_plasmagun 1
set disable_weapon_bfg 1
set disable_ammo_shells 1
set disable_ammo_bullets 1
set disable_ammo_grenades 1
set disable_ammo_cells 1
set disable_ammo_lightning 1
set disable_ammo_rockets 1
set disable_ammo_slugs 1
set disable_ammo_bfg 1
set disable_item_armor_shard 1
set disable_item_armor_combat 1
set disable_item_armor_body 1
set disable_item_health_small 1
set disable_item_health 1
set disable_item_health_large 1
set disable_item_health_mega 1
set disable_item_quad 1

addbot Xaero 5
addbot Xaero 5
addbot Xaero 5
addbot Xaero 5
addbot Xaero 5
addbot Xaero 5
addbot Xaero 5

Start a server through command line:

./q3ded +set sv_pure 0 +set vm_game 0 +devmap battleforged +set g_gametype 3 +exec disable.cfg

After connecting to a server, restart the map through map_restart and wait, untill it crashes. I sped up game with timescale 100 and sv_fps 250, so I can observe crash after about 10 seconds of watching bots playing.

Why it's crashing

When an item is disabled through a cvar, the item field of gentity_t is left NULL. RespawnItem wants to respawn an item and tries to dereference nullish ent->item, which leads to segmentation violation. This is also true for "teamed" items, where a random picked item from the "team" could be disabled, thus have nullish ent->item.

[ec-]

fixed in 9503efa