session BUGFIX check for errors when generating capabilities

Fixes #271

Author: michalvasko

src/session.c

@@ -1287,6 +1287,9 @@ nc_send_hello_io(struct nc_session *session)
         sid = NULL;
     } else {
         cpblts = nc_server_get_cpblts_version(session->ctx, LYS_VERSION_1);
+        if (!cpblts) {
+            return NC_MSG_ERROR;
+        }
 
         io_timeout = NC_SERVER_HELLO_TIMEOUT * 1000;
         sid = &session->id;