reiserfscore: fix "new_insert_key may be used uninitialized..."

new_insert_key only makes any sense when it's associated with a
new_insert_ptr, which is initialized to NULL and changed to a
buffer_head when we also initialize new_insert_key.  We can key off
of that to avoid the uninitialized warning.

Signed-off-by: Jeff Mahoney <jeffm@suse.com>

reiserfscore/ibalance.c

@@ -881,8 +881,9 @@ int balance_internal(struct tree_balance *tb,	/* tree_balance structure
 					       insert_key, insert_ptr);
 	}
 
-	memcpy(new_insert_key_addr, &new_insert_key, KEY_SIZE);
 	insert_ptr[0] = new_insert_ptr;
+	if (new_insert_ptr)
+		memcpy(new_insert_key_addr, &new_insert_key, KEY_SIZE);
 
 	return order;
 }