ensure that inner HTTP response doesn't outlive the callback

Life span of the pointer to inner response might accidentally leak to
query callback (e.g. retry happened, but the query operation has timed
out)

Change-Id: Ie5959c004e858f3bd4e15d4835c05ee80322b35b
Reviewed-on: http://review.couchbase.org/c/libcouchbase/+/153040
Reviewed-by: Brett Lawson <brett19@gmail.com>
Tested-by: Build Bot <build@couchbase.com>

src/n1ql/n1ql.cc

@@ -325,6 +325,7 @@ typedef struct lcb_QUERY_HANDLE_ : lcb::jsparse::Parser::Actions {
         if (lasterr == LCB_SUCCESS) {
             lasterr = LCB_ERR_TIMEOUT;
         }
+        cur_htresp = nullptr;
         delete this;
     }
     lcb::io::Timer<lcb_QUERY_HANDLE_, &lcb_QUERY_HANDLE_::on_timeout> timer;
@@ -641,7 +642,7 @@ void N1QLREQ::invoke_row(lcb_RESPQUERY *resp, bool is_last)
     resp->handle = this;
 
     if (resp->htresp) {
-        resp->ctx.http_response_code = cur_htresp->ctx.response_code;
+        resp->ctx.http_response_code = resp->htresp->ctx.response_code;
         resp->ctx.endpoint = resp->htresp->ctx.endpoint;
         resp->ctx.endpoint_len = resp->htresp->ctx.endpoint_len;
     }
@@ -739,6 +740,7 @@ static void chunk_callback(lcb_INSTANCE *instance, int ign, const lcb_RESPBASE *
         return;
     }
     req->parser->feed(static_cast<const char *>(rh->ctx.body), rh->ctx.body_len);
+    req->cur_htresp = nullptr;
 }
 
 void N1QLREQ::fail_prepared(const lcb_RESPQUERY *orig, lcb_STATUS err)