buffered_file: reuse QEMUFile has_error field Instead of having two has_error fields in QEMUFile & QEMUBufferedFile, reuse the 1st one. Notice that the one in buffered_file is only set after a file operation. Signed-off-by: Juan Quintela <quintela@redhat.com> Reviewed-by: Anthony Liguori <aliguori@us.ibm.com>