Avoid raising an unhandled exception

guix-data-service/jobs/load-new-guix-revision.scm

@@ -2929,7 +2929,13 @@ WHERE builder != 'builtin:download'
     ;; Prompt getting the guix-revision-id as soon as possible
     (spawn-fiber
      (lambda ()
-       (fibers-force guix-revision-id-promise)))
+       (with-exception-handler
+           (lambda _
+             ;; Silently handle this exception
+             #f)
+         (lambda ()
+           (fibers-force guix-revision-id-promise))
+         #:unwind? #t)))
 
     (let* ((guix-source
             channel-derivations-by-system