Merge remote-tracking branch 'remotes/armbru/tags/pull-misc-2019-03-26' into staging

Miscellaneous patches for 2019-03-26

# gpg: Signature made Tue 26 Mar 2019 07:10:23 GMT
# gpg:                using RSA key 3870B400EB918653
# gpg: Good signature from "Markus Armbruster <armbru@redhat.com>" [full]
# gpg:                 aka "Markus Armbruster <armbru@pond.sub.org>" [full]
# Primary key fingerprint: 354B C8B3 D7EB 2A6B 6867  4E5F 3870 B400 EB91 8653

* remotes/armbru/tags/pull-misc-2019-03-26:
  qapi/qmp-dispatch: fix return value in do_qmp_dispatch
  json: Fix off-by-one assert check in next_state()
  xen-block: Replace qdict_put_obj() by qdict_put() where appropriate
  util/error: Remove an unnecessary NULL check

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>