fix issue #949 - dropping welded iron ball

If punished and the attached iron ball was both cursed and wielded,
falling while going down stairs would drop it instead of leaving it
welded to hero's hand. ( Didn't happen for iron ball that wasn't
chained to hero's leg.)

I thought that this was going to be a one or two line fix but ball
and chain stuff is never that simple.

Fixes #949

src/do.c

@@ -595,6 +595,19 @@ canletgo(struct obj *obj, const char *word)
             Norep("You cannot %s %s you are wearing.", word, something);
         return FALSE;
     }
+    if (obj == uwep && welded(uwep)) {
+        /* no weldmsg(), so uwep->bknown might become set silently
+           if word is "" */
+        if (*word) {
+            const char *hand = body_part(HAND);
+
+            if (bimanual(uwep))
+                hand = makeplural(hand);
+            Norep("You cannot %s %s welded to your %s.", word, something,
+                  hand);
+        }
+        return FALSE;
+    }
     if (obj->otyp == LOADSTONE && obj->cursed) {
         /* getobj() kludge sets corpsenm to user's specified count
            when refusing to split a stack of cursed loadstones */
@@ -1612,7 +1625,8 @@ goto_level(
                 You("fall down the %s.", ga.at_ladder ? "ladder" : "stairs");
                 if (Punished) {
                     drag_down();
-                    ballrelease(FALSE);
+                    if (!welded(uball))
+                        ballrelease(FALSE);
                 }
                 /* falling off steed has its own losehp() call */
                 if (u.usteed)
@@ -1632,7 +1646,7 @@ goto_level(
     } else { /* trap door or level_tele or In_endgame */
         u_on_rndspot((up ? 1 : 0) | (was_in_W_tower ? 2 : 0));
         if (falling) {
-            if (Punished)
+            if (Punished && !welded(uball))
                 ballfall();
             selftouch("Falling, you");
             do_fall_dmg = TRUE;