BUG/MINOR: config: Check buffer pool creation for failures

The call to init_buffer() during the worker startup may fail. In that case,
an error message is displayed but the error was not properly handled. So
let's add the proper check and exit on error.

src/haproxy.c

@@ -2347,7 +2347,8 @@ static void step_init_2(int argc, char** argv)
 		deinit_and_exit(0);
 
 	/* now we know the buffer size, we can initialize the channels and buffers */
-	init_buffer();
+	if (!init_buffer())
+		exit(1); // error already reported
 
 	list_for_each_entry(pcf, &post_check_list, list) {
 		err_code |= pcf->fct();