fix: corpses disappearing outside the player's PVS

[Vladislav4KZ]

Fixes: #192

[Vladislav4KZ]

I replaced the FTENT_COLLIDEALL flag with FTENT_PERSIST after looking at the disassembled client.so code from CS 1.6, where this flag was not present.

Although, thinking about it now, it was probably added intentionally so that corpses wouldn’t get stuck on players or something like that.

[Vladislav4KZ]

I still don’t understand this: if the FTENT_COLLIDEALL flag was present in the CS16Client code, why was the FTENT_COLLIDEWORLD flag needed then?

[Velaron]

Maybe it was added before I implemented FTENT_BODYTRACE, maybe just a typo, don't remember.