fix #K3917 - fuzzer stuck in endless lifesave loop

Life-saving from being burned up in lava attempts to teleport the
hero to safely.  If that fails, hero immediately burns up again.
For fuzz testing, that results in an infinite loop.

While implementing a fix (in done(), not just lava-specific), I
noticed that hangup while running interactively in explore or
wizard mode could be subject to similar effect.

For the fuzzer, if hero dies 15 times without advancing the move
count (not 'moves', the turn count), don't life-save again.  With
hangup, don't prompt for "Die?" more than once.

Normal interactive declining to die still works.  The more exotic
situations aren't tested.

src/decl.c

@@ -320,6 +320,8 @@ const struct instance_globals_d g_init_d = {
     0, /* did_nothing_flag */
     /* dog.c */
     DUMMY, /* dogname */
+    /* end.c */
+    0L, /* done_seq */
     /* mon.c */
     FALSE, /* disintegested */
     /* o_init.c */

src/end.c

@@ -1173,8 +1173,23 @@ done(int how)
         bot();
     }
 
+    /* hero_seq is (moves<<3 + n) where n is number of moves made
+       by the hero on the current turn (since the 'moves' variable
+       actually counts turns); its details shouldn't matter here */
+    if (gd.done_seq < gh.hero_seq)
+        gd.done_seq = gh.hero_seq;
+
     if (iflags.debug_fuzzer) {
-        if (!(gp.program_state.panicking || how == PANICKED)) {
+        if (!gp.program_state.panicking && how != PANICKED
+            /* Guard against getting stuck in a loop if we die in one of
+             * the few ways where life-saving isn't effective (cited case
+             * was burning in lava when the level was too full to allow
+             * teleporting to safety).  Skip the life-save attempt if we've
+             * died on the same move more than 15 times; give up instead.
+             * (Note: theoretically we could get killed more than that in
+             * one move if there are multiple fast monsters with multiple
+             * attacks against a wimply hero, or a ton of ranged attacks.) */
+            && (gd.done_seq++ < gh.hero_seq + 15L)) {
             savelife(how);
             /* periodically restore characteristics and lost exp levels
                or cure lycanthropy */
@@ -1192,7 +1207,8 @@ done(int how)
             gk.killer.format = 0;
             return;
         }
-    } else
+    }
+
     if (how == ASCENDED || (!gk.killer.name[0] && how == GENOCIDED))
         gk.killer.format = NO_KILLER_PREFIX;
     /* Avoid killed by "a" burning or "a" starvation */
@@ -1237,6 +1253,12 @@ done(int how)
     }
     /* explore and wizard modes offer player the option to keep playing */
     if (!survive && (wizard || discover) && how <= GENOCIDED
+#ifdef HANGUPHANDLING
+        /* if hangup has occurred, the only possible answer to a paranoid
+           query is 'no'; we want 'no' as the default for "Die?" but can't
+           accept it more than once if there's no user supplying it */
+        && !(gp.program_state.done_hup && gd.done_seq++ == gh.hero_seq)
+#endif
         && !paranoid_query(ParanoidDie, "Die?")) {
         pline("OK, so you don't %s.", (how == CHOKING) ? "choke" : "die");
         iflags.last_msg = PLNMSG_OK_DONT_DIE;