Merge branch 'fix-uchex-warnings'

There is one more report that is false positive, see [1]:
  "In bufferevent_openssl.c, pointer wm is dereferenced on line 871
before it is null checked on line 873."

  [1]: https://github.com/libevent/libevent/issues/382#issuecomment-238081938

* fix-uchex-warnings:
  evdns: do not check server_req twice
  evrpc: do not check req twice

Fixes: #382