row_purge_upd_exist_or_extern_func(): Check for node->vcol_op_failed()
after row_purge_remove_sec_if_poss(), like row_purge_del_mark() did.
This avoids us dereferencing the node->table=NULL pointer.

The test case, submitted by Elena Stepanova, is not deterministic and
does not repeat the bug on 10.2. With the added loop, for me, it reliably
crashes 10.3 without the fix. I was unable to create a deterministic
test case for either 10.2 or 10.3.

Reviewed by Thirunarayanan Balathandayuthapani