url_encoding: Unset pointers on error
url_encoding: Unset pointers on error

Caught this when lcb_make_http_request crashed on double free in the
case of an error.

Change-Id: I40d9bbc627c7856b3a43bfaef407b386fc352ccb
Reviewed-on: http://review.couchbase.org/45150
Tested-by: Mark Nunberg <e7d42768707bf23038325b0b68d4b577e5f6064a@haskalah.org>
Reviewed-by: Sergey Avseyev <87f6d5e4fd3644c3c20800cde7fd3ad1569370b3@gmail.com>

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