Handle the case where client_service::remove_fragments() fails,
for reasons other than bf abort. In this case, we want to make
sure that the transaction state is moved to s_must_abort, so
that we satisfy the sanity check at the end of before_prepare():
```
assert(state() == s_preparing ||
(is_xa() && state() == s_replaying) ||
(ret && (state() == s_must_abort ||
state() == s_must_replay ||
state() == s_cert_failed ||
state() == s_aborted)));
```