vmstate_load_state return error into virtio_load function

Qemu version 4.2.1

In the function of virtio_load, the vmstate_load_state will return error in the following case.

The virtio is legacy mode(disable-modern=on,disable-legacy=off), virtio_device is in reset state. 

In the the function of "vmstate_load_state", it will load all subsection. For the vmstate_virtio_extra_state subsection. 
It will execute:
vmstate_load_state   -->
          ret = field->info->get(f, curr_elem, size, field);    line 143  vmstate.c.
           -->virtio_pci_load_extra_state
                        -->  vmstate_load_state
                                 -->qemu_peek_byte
But if the f->buf_index is same with buf_size, qemu_peek_byte function will set "-EIO" error. 
the field->info->get will return 0, then it will get the error "ret = qemu_file_get_error(f);". then the vmstate_load_state will return error.

It output is "Failed to load virtio/extra_state:extra_state"