More long worm checks when splitting

When a long worm is split into two, perform more checks placing
the segments on the map.

src/worm.c

@@ -415,7 +415,7 @@ struct obj *weap;
     wgrowtime[new_wnum] = 0L;    /* trying to call initworm().       */
 
     /* Place the new monster at all the segment locations. */
-    place_wsegs(new_worm);
+    place_wsegs(new_worm, worm);
 
     if (context.mon_moving)
         pline("%s is cut in half.", Monnam(worm));
@@ -556,17 +556,28 @@ int fd;
  *  place_wsegs()
  *
  *  Place the segments of the given worm.  Called from restore.c
+ *  If oldworm is not NULL, assumes the oldworm segments are on map
+ *  in the same location as worm segments
  */
 void
-place_wsegs(worm)
-struct monst *worm;
+place_wsegs(worm, oldworm)
+struct monst *worm, *oldworm;
 {
     struct wseg *curr = wtails[worm->wormno];
 
     /*  if (!mtmp->wormno) return;  bullet proofing */
 
     while (curr != wheads[worm->wormno]) {
-        place_worm_seg(worm, curr->wx, curr->wy);
+        xchar x = curr->wx;
+        xchar y = curr->wy;
+
+        if (oldworm) {
+            if (m_at(x,y) == oldworm)
+                remove_monster(x, y);
+            else
+                impossible("placing worm seg <%i,%i> over another mon", x, y);
+        }
+        place_worm_seg(worm, x, y);
         curr = curr->nseg;
     }
 }