u.uswallow

Make sure u.uswallow is cleared when u.ustuck gets set to Null so
that they won't be out of sync with each other.  Having u.uswallow
be non-zero does imply that u.ustuck is non-Null.

Running #panic while swallowed didn't produce any anomalies for me,
either before or after this change.

src/do.c

@@ -1442,8 +1442,7 @@ goto_level(
         unplacebc();
     reset_utrap(FALSE); /* needed in level_tele */
     fill_pit(u.ux, u.uy);
-    set_ustuck((struct monst *) 0); /* idem */
-    u.uswallow = u.uswldtim = 0;
+    set_ustuck((struct monst *) 0); /* clear u.ustuck and u.uswallow */
     set_uinwater(0); /* u.uinwater = 0 */
     u.uundetected = 0; /* not hidden, even if means are available */
     keepdogs(FALSE);

src/mon.c

@@ -2952,7 +2952,7 @@ monkilled(
 }
 
 void
-set_ustuck(struct monst* mtmp)
+set_ustuck(struct monst *mtmp)
 {
     if (iflags.sanity_check || iflags.debug_fuzzer) {
         if (mtmp && !next2u(mtmp->mx, mtmp->my))
@@ -2962,23 +2962,26 @@ set_ustuck(struct monst* mtmp)
 
     g.context.botl = 1;
     u.ustuck = mtmp;
+    if (!u.ustuck) {
+        u.uswallow = 0;
+        u.uswldtim = 0;
+    }
 }
 
 void
-unstuck(struct monst* mtmp)
+unstuck(struct monst *mtmp)
 {
     if (u.ustuck == mtmp) {
         struct permonst *ptr = mtmp->data;
+        unsigned swallowed = u.uswallow;
 
         /* do this first so that docrt()'s botl update is accurate;
-           safe to do as long as u.uswallow is also cleared before docrt() */
+           clears u.uswallow as well as setting u.ustuck to Null */
         set_ustuck((struct monst *) 0);
 
-        if (u.uswallow) {
+        if (swallowed) {
             u.ux = mtmp->mx;
             u.uy = mtmp->my;
-            u.uswallow = 0;
-            u.uswldtim = 0;
             if (Punished && uchain->where != OBJ_FLOOR)
                 placebc();
             g.vision_full_recalc = 1;

src/save.c

@@ -183,7 +183,7 @@ dosave0(void)
     /* these pointers are no longer valid, and at least u.usteed
      * may mislead place_monster() on other levels
      */
-    set_ustuck((struct monst *) 0);
+    set_ustuck((struct monst *) 0); /* also clears u.uswallow */
     u.usteed = (struct monst *) 0;
 
     for (ltmp = (xint8) 1; ltmp <= maxledgerno(); ltmp++) {

src/teleport.c

@@ -354,6 +354,7 @@ teleok(coordxy x, coordxy y, boolean trapok)
 void
 teleds(coordxy nux, coordxy nuy, int teleds_flags)
 {
+    unsigned was_swallowed;
     boolean ball_active, ball_still_in_range = FALSE,
             allow_drag = (teleds_flags & TELEDS_ALLOW_DRAG) != 0,
             is_teleport = (teleds_flags & TELEDS_TELEPORT) != 0;
@@ -391,6 +392,7 @@ teleds(coordxy nux, coordxy nuy, int teleds_flags)
             unplacebc(); /* have to move the ball */
     }
     reset_utrap(FALSE);
+    was_swallowed = u.uswallow; /* set_ustuck(Null) clears uswallow */
     set_ustuck((struct monst *) 0);
     u.ux0 = u.ux;
     u.uy0 = u.uy;
@@ -400,9 +402,7 @@ teleds(coordxy nux, coordxy nuy, int teleds_flags)
         g.youmonst.m_ap_type = M_AP_NOTHING;
     }
 
-    if (u.uswallow) {
-        /* subset of unstuck() */
-        u.uswldtim = u.uswallow = 0;
+    if (was_swallowed) {
         if (Punished) { /* ball&chain are off map while swallowed */
             ball_active = TRUE; /* to put chain and non-carried ball on map */
             ball_still_in_range = allow_drag = FALSE; /* (redundant) */