Short circuit friend list error (#1805)

Co-authored-by: kraflab <[email protected]>

src/p_enemy.c

@@ -944,6 +944,17 @@ static boolean P_LookForMonsters(mobj_t *actor, boolean allaround)
       current_actor = actor;
       current_allaround = allaround;
 
+      // There is a bug in cl11+ that causes the player to get added
+      //   to the monster friend list when damaged to below 50% health.
+      // This causes all monsters to believe friend monsters exist.
+      // The search algorithm is expensive and massively so on maps with many monsters.
+      // We still need to match rng calls for demo sync, but PIT_FindTarget is a no op.
+      if (((mobj_t *) cap->cnext)->player && cap->cnext == cap->cprev)
+      {
+        P_Random(pr_friends);
+        return false;
+      }
+
       // Search first in the immediate vicinity.
 
       if (!P_BlockThingsIterator(x, y, PIT_FindTarget))