Fix ball and chain sanity

Scatter did not consider the ball or chain, and moved them around, causing
ball and chain sanity error.

One way to trigger was being punished, with chain on a land mine and having
a monster trigger the mine. Now the chain will shatter, unpunishing the hero.

doc/fixes36.3

@@ -177,6 +177,7 @@ avoid 'object lost' panic when polymorph causes loss of levitation boots or
 	over but buffered output didn't show it until hero stopped, so it
 	wasn't possible to tell where they were, unlike all other forms of
 	multiple movement; stop running if/when an engraving is reached
+fix exploding land mine moving ball or chain and causing a sanity error
 
 
 Fixes to Post-3.6.2 Problems that Were Exposed Via git Repository

src/explode.c

@@ -621,6 +621,13 @@ struct obj *obj; /* only scatter this obj        */
                    obj->ox, obj->oy, sx, sy);
 
     while ((otmp = (individual_object ? obj : level.objects[sx][sy])) != 0) {
+        if (otmp == uball || otmp == uchain) {
+            boolean waschain = (otmp == uchain);
+            pline_The("chain shatters!");
+            unpunish();
+            if (waschain)
+                continue;
+        }
         if (otmp->quan > 1L) {
             qtmp = otmp->quan - 1L;
             if (qtmp > LARGEST_INT)