fix issue #1434 - engulfed gas spore explosion

Issue reported by Umbire:  a gas spore that got swallowed and killed
didn't die but exploded anyway, with the explosion affecting the map
instead of being contained in the swallower.

There was code to handle that but it wasn't being executed.  This fix
feels unclean but seems to work.

I couldn't reproduce the survival of the gas spore but since that
isn't wanted I won't worry about it.

Fixes #1434

src/mon.c

@@ -2204,8 +2204,7 @@ mfndpos(
             if (IS_DOOR(ntyp)
                 /* an amorphous creature can only move under/through a
                    closed door if it doesn't currently have hero engulfed */
-                && !((amorphous(mdat) || can_fog(mon))
-                     && (mon != u.ustuck || !u.uswallow))
+                && !((amorphous(mdat) || can_fog(mon)) && !engulfing_u(mon))
                 && (((levl[nx][ny].doormask & D_CLOSED) && !(flag & OPENDOOR))
                     || ((levl[nx][ny].doormask & D_LOCKED)
                         && !(flag & UNLOCKDOOR))) && !thrudoor)
@@ -2670,11 +2669,25 @@ mon_leaving_level(struct monst *mon)
             remove_monster(mx, my);
 
 #if 0   /* mustn't do this; too many places assume that the stale
-           monst->mx,my values are still valid */
+         * monst->mx,my values are still valid */
         mon->mx = mon->my = 0; /* off normal map */
 #endif
     }
     if (onmap) {
+        /* gulpmm() tries to deal with this, but without this extra
+           place_monster() the messages for exploding engulfed gas spore
+           are delivered without the engulfer being shown on the map */
+        if (gm.mswallower && gm.mswallower != mon) {
+            if (gm.mswallower != &gy.youmonst) {
+                place_monster(gm.mswallower,
+                              gm.mswallower->mx, gm.mswallower->my);
+            } else {
+                u_on_newpos(u.ux, u.uy);
+                if (canspotself())
+                    display_self();
+            }
+        }
+
         mon->mundetected = 0; /* for migration; doesn't matter for death */
         /* unhide mimic in case its shape has been blocking line of sight
            or it is accompanying the hero to another level */
@@ -3146,6 +3159,9 @@ corpse_chance(
     struct permonst *mdat = mon->data;
     int i, tmp;
 
+    if (!magr && gm.mswallower && attacktype(gm.mswallower->data, AT_ENGL))
+        magr = gm.mswallower, was_swallowed = TRUE; /* for gas spore boom */
+
     if (mdat == &mons[PM_VLAD_THE_IMPALER] || mdat->mlet == S_LICH) {
         if (cansee(mon->mx, mon->my) && !was_swallowed)
             pline_mon(mon, "%s body crumbles into dust.",
@@ -3162,7 +3178,10 @@ corpse_chance(
                 tmp = d((int) mdat->mlevel + 1, (int) mdat->mattk[i].damd);
             else
                 tmp = 0;
+
             if (was_swallowed && magr) {
+                /* mdef is a gas spore (AT_BOOM) that is exploding inside an
+                   engulfer; suppress usual explosion since it's contained */
                 if (magr == &gy.youmonst) {
                     There("is an explosion in your %s!", body_part(STOMACH));
                     Sprintf(svk.killer.name, "%s explosion",
@@ -3176,14 +3195,11 @@ corpse_chance(
                         mondied(magr);
                     if (DEADMONSTER(magr)) { /* maybe lifesaved */
                         if (canspotmon(magr))
-                            pline_mon(magr, "%s rips open!",
-                                      Monnam(magr));
+                            pline_mon(magr, "%s rips open!", Monnam(magr));
                     } else if (canseemon(magr))
-                        pline_mon(magr,
-                                  "%s seems to have indigestion.",
+                        pline_mon(magr, "%s seems to have indigestion.",
                                   Monnam(magr));
                 }
-
                 return FALSE;
             }