Add sanity checking for long worms

include/extern.h

@@ -2761,6 +2761,7 @@ E void FDECL(detect_wsegs, (struct monst *, BOOLEAN_P));
 E void FDECL(save_worm, (int, int));
 E void FDECL(rest_worm, (int));
 E void FDECL(place_wsegs, (struct monst *));
+E void FDECL(sanity_check_worm, (struct monst *));
 E void FDECL(remove_worm, (struct monst *));
 E void FDECL(place_worm_tail_randomly, (struct monst *, XCHAR_P, XCHAR_P));
 E int FDECL(size_wseg, (struct monst *));

src/mon.c

@@ -93,6 +93,8 @@ mon_sanity_check()
         else if (level.monsters[x][y] != mtmp)
             impossible("mon (%s) at <%d,%d> is not there!",
                        fmt_ptr((genericptr_t) mtmp), x, y);
+        else if (mtmp->wormno)
+            sanity_check_worm(mtmp);
     }
 
     for (x = 0; x < COLNO; x++)

src/worm.c

@@ -569,6 +569,28 @@ struct monst *worm;
     }
 }
 
+void
+sanity_check_worm(worm)
+struct monst *worm;
+{
+    struct wseg *curr;
+
+    if (!worm)
+        panic("no worm!");
+    if (!worm->wormno)
+        panic("not a worm?!");
+
+    curr = wtails[worm->wormno];
+
+    while (curr != wheads[worm->wormno]) {
+        if (!isok(curr->wx, curr->wy))
+            panic("worm seg not isok");
+        if (level.monsters[curr->wx][curr->wy] != worm)
+            panic("worm not at seg location");
+        curr = curr->nseg;
+    }
+}
+
 /*
  *  remove_worm()
  *