Fix bug with stack corruption

See same [here](http://gitlab.kawaz.org/giginet/cocos2d-x/commit/d0c35f28557c081dfc58c4bd0562cf20e59ba3f0)

Also:
> update: I have little theory that I will try to confirm tonight, curl implementation in some methods called from crashing _httplibcurl.cpp (for example curl_easy_getinfo) does va_start but doesn't do va_end...
according to the docs va_end MUST be called. some people say it could corrupt stack, still I don't get why debug build doesn't have the problem

[Original](http://jira.phoenixviewer.com/browse/FIRE-11943), but `libcurl` source _does_ have `va_end`.