vhost: Do not abort on log-start error

vhost: Do not abort on log-start error

Commit 3688fec8923 ("memory: Add Error** argument to .log_global_start()
handler") enabled vhost_log_global_start() to return a proper error, but
did not change it to do so; instead, it still aborts the whole process
on error.

This crash can be reproduced by e.g. killing a virtiofsd daemon before
initiating migration.  In such a case, qemu should not crash, but just
make the attempted migration fail.

Buglink: https://issues.redhat.com/browse/RHEL-94534
Reported-by: Tingting Mao <timao@redhat.com>
Signed-off-by: Hanna Czenczek <hreitz@redhat.com>
Message-Id: <20250724125928.61045-2-hreitz@redhat.com>
Reviewed-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Tested-by: Lei Yang <leiyang@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
(cherry picked from commit c1997099dc26d95eb9f2249f2894aabf4cf0bf8b)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>