py: Clear allocated, but unused memory in containers.

Also, clear up freed slots in containers.

As a follow up to 32bef315be8e56ad2d7f69223fe7b9606893b6ab.
diff --git a/py/objarray.c b/py/objarray.c
index ce107dd..ea37655 100644
--- a/py/objarray.c
+++ b/py/objarray.c
@@ -125,6 +125,7 @@
         // TODO: alloc policy
         self->free = 8;
         self->items = m_realloc(self->items,  item_sz * self->len, item_sz * (self->len + self->free));
+        mp_seq_clear(self->items, self->len + 1, self->len + self->free, item_sz);
     }
     mp_binary_set_val_array(self->typecode, self->items, self->len++, arg);
     self->free--;