lcb_create(): do not poison argument on failures
lcb_create(): do not poison argument on failures

Ruby client was relying that the pointer will remain NULL in case of
lcb_create() failure, and trying to call lcb_destroy() with invalid
memory on GC. I've fixed ruby side to NULL the pointer on failures,
but it is also makes sense not to touch it unless lcb_create() return
LCB_SUCCESS.

Change-Id: I86d1856ee403ef411a0c7e9df93add8a995156f8
Reviewed-on: http://review.couchbase.org/27636
Tested-by: Sergey Avseyev <87f6d5e4fd3644c3c20800cde7fd3ad1569370b3@gmail.com>
Reviewed-by: Trond Norbye <60edd2ef23891a753f231b0c6f161dc634079a93@gmail.com>

uvenum/libcouchbase,trondn/libcouchbase,PureSwift/libcouchbase,PureSwift/libcouchbase,maxim-ky/libcouchbase,signmotion/libcouchbase,kojiromike/libcouchbase,avsej/libcouchbase,senthilkumaranb/libcouchbase,trondn/libcouchbase,signmotion/libcouchbase,PureSwift/libcouchbase,mnunberg/libcouchbase,avsej/libcouchbase,uvenum/libcouchbase,trondn/libcouchbase,senthilkumaranb/libcouchbase,mnunberg/libcouchbase,maxim-ky/libcouchbase,mody/libcouchbase,kojiromike/libcouchbase,senthilkumaranb/libcouchbase,couchbase/libcouchbase,avsej/libcouchbase,uvenum/libcouchbase,senthilkumaranb/libcouchbase,uvenum/libcouchbase,mody/libcouchbase,mnunberg/libcouchbase,couchbase/libcouchbase,maxim-ky/libcouchbase,mody/libcouchbase,avsej/libcouchbase,mnunberg/libcouchbase,mnunberg/libcouchbase,avsej/libcouchbase,kojiromike/libcouchbase,avsej/libcouchbase,kojiromike/libcouchbase,mody/libcouchbase,couchbase/libcouchbase,couchbase/libcouchbase,trondn/libcouchbase,avsej/libcouchbase,couchbase/libcouchbase,uvenum/libcouchbase,maxim-ky/libcouchbase,PureSwift/libcouchbase,couchbase/libcouchbase,signmotion/libcouchbase,couchbase/libcouchbase,trondn/libcouchbase,signmotion/libcouchbase