Bug #11019 mgmapi start backup in some cases returns wrong backupid

ndb/include/mgmapi/mgmapi.h

@@ -915,6 +915,8 @@ extern "C" {
    * @param   backup_id       Backup ID is returned from function.
    * @param   reply           Reply message.
    * @return                  -1 on error.
+   * @note                    backup_id will not be returned if
+   *                          wait_completed == 0
    */
   int ndb_mgm_start_backup(NdbMgmHandle handle, int wait_completed,
 			   unsigned int* backup_id,

ndb/src/mgmsrv/Services.cpp

@@ -671,7 +671,8 @@ MgmApiSession::startBackup(Parser<MgmApiSession>::Context &,
   }
   else{
     m_output->println("result: Ok");
-    m_output->println("id: %d", backupId);
+    if (completed)
+      m_output->println("id: %d", backupId);
   }
   m_output->println("");
   DBUG_VOID_RETURN;