Explosions don't dissipate after hitting a death pit

If you jump a minecart off into a deathpit, its explosion will never go away.

One theory I came up with on Discord hours earlier is that it could be the item is constantly "dying" because it is contact with the death pit. As in: Touch death pit -> start death animation, next tic -> still touching death pit -> start death animation again, etc

I believe I may have found the culprit, but I don't have time to compile and test right now. It seems like @MonsterIestyn had the same suspicions as me about the animation resetting, but this doesn't happen, nor does it need to -- because the state cycle is never allowed to run at all.

In P_MobjThinker, a check is performed where P_ZMovement is run -- if it returns false, the thinker ends. This happens before the state cycle is performed, and therefore objects that don't pass the check won't complete their animations and state behaviors.

The issue is that, inside P_ZMovement, a check is run to see if the object has collided with a deathpit. If so, it always returns false. But it does not always remove the object.

The MobjThinker fallaciously assumes that the object was removed without P_MobjWasRemoved(mobj) being checked, and it ends the thinker prematurely based on that assumption. The object never disappears because the thinker never gets to advance the state cycle.

My working theory is that this can be easily resolved by changing https://git.do.srb2.org/STJr/SRB2/blob/next/src/p_mobj.c#L2494 to return P_MobjWasRemoved(mo). This should allow the thinker to run its course, thus letting the animation finish.

mentioned in merge request !1688 (merged)

closed with merge request !1688 (merged)

mentioned in commit 4e972f7d