proto/zeromq: Don't leak ub on write error in uwsgi_proto_zeromq_writev_header

Reported by Coverity as CID #971247.
plugins/http: fixup some leaks in spdy

Reported by Coverity as CID #971245, #971246.
Merge pull request #143 from xrmx/coverity6

Fix some leaks reported by Coverity scan