libxl: preserve errno in libxl__xcinfo2xlinfo()

Callers observing errors elsewhere may be confused by the ENOSYS that
the Flask operation would yield on a Flask-disabled hypervisor.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Jason Andryuk <jason.andryuk@amd.com>
Acked-by: Anthony PERARD <anthony.perard@vates.tech>

tools/libs/light/libxl_domain.c

@@ -277,6 +277,7 @@ void libxl__xcinfo2xlinfo(libxl_ctx *ctx,
                           libxl_dominfo *xlinfo)
 {
     size_t size;
+    int saved_errno = errno;
 
     memcpy(&(xlinfo->uuid), xcinfo->handle, sizeof(xen_domain_handle_t));
     xlinfo->domid = xcinfo->domain;
@@ -284,6 +285,7 @@ void libxl__xcinfo2xlinfo(libxl_ctx *ctx,
     if (libxl_flask_sid_to_context(ctx, xlinfo->ssidref,
                                    &xlinfo->ssid_label, &size) < 0)
         xlinfo->ssid_label = NULL;
+    errno = saved_errno;
 
     xlinfo->dying      = !!(xcinfo->flags&XEN_DOMINF_dying);
     xlinfo->shutdown   = !!(xcinfo->flags&XEN_DOMINF_shutdown);