Spotted by ASAN when 'make check'.

Signed-off-by: Li Qiang <liq3ea@163.com>
Message-Id: <20190310160227.103090-1-liq3ea@163.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Fixes: fc281c80
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>