Fixed a crash when user has cl_bloodtype set to 2 and an actor has undefined blood type

As mentioned in https://zandronum.com/tracker/view.php?id=4341, if an actor has an unknown or invalid bloodtype and the user has set cl_bloodtype to 2, the game will crash when the actor bleeds because of a null pointer being referenced. This was already fixed in (G)ZDoom: https://github.com/ZDoom/gzdoom/commit/9435cdc5c9d18100fa8a8a7cbe37cd705080220b

Transplanting this commit was pretty easy (some manual work was needed because of our own code changes), and it was made not too long after GZDoom 1.8.6 was released, which we're currently based on.