qemu-char: retry g_poll on EINTR This is a case where pty_chr_update_read_handler_locked's lack of error checking can produce incorrect values. We are not using SIGUSR1 anymore, so this is quite theoretical, but easy to fix. Reported-by: Markus Armbruster <armbru@redhat.com> Reviewed-by: Markus Armbruster <armbru@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>