Cache model in-game may cause memory corruption

[alexey-lysiuk]

Extract entities file from start@9788.ent.zip into id1/maps, and start a new game. Pick silver key to observe the issue.
The following two edicts were added to entities lump extracted from Quake 1.06.

{
"classname" "item_key1"
"origin" "544 434 24"
"target" "spawn_notnull"
}
{
"classname" "info_notnull"
"origin" "544 654 -40"
"targetname" "spawn_notnull"
"use" "item_cells"
}

For me, game usually hangs because of kinda infinite loop.

The problem boils down to loading of model during execution of SV_TouchLinks() function. It does Hunk_LowMark() at the beginning, and Hunk_FreeToLowMark() at the end effectively corrupting memory of loaded model.