MINOR: cli: use the new buffer API

Almost nothing required to be touched.
diff --git a/src/cli.c b/src/cli.c
index c34078f..c656e4b 100644
--- a/src/cli.c
+++ b/src/cli.c
@@ -730,7 +730,7 @@
 			 * buffer is empty. This still allows pipelined requests
 			 * to be sent in non-interactive mode.
 			 */
-			if ((res->flags & (CF_SHUTW|CF_SHUTW_NOW)) || (!(appctx->st1 & APPCTX_CLI_ST1_PROMPT) && !req->buf->o)) {
+			if ((res->flags & (CF_SHUTW|CF_SHUTW_NOW)) || (!(appctx->st1 & APPCTX_CLI_ST1_PROMPT) && !co_data(req))) {
 				appctx->st0 = CLI_ST_END;
 				continue;
 			}