bug#43518: Guix substitute crash in procedure raise-exception: wrong type agument in position 1: #f

[Maxim Cournoyer]

Seems like a second exception raised in the process of raising an
exception :-).

The original crash reason is unkown, the network was operating normally.

downloading from 
http://127.0.0.1:8080/nar/gzip/8sdx7qyb4l3ni6yy902jlhamb26lqb6f-spice-gtk-0.37 
...


0.0 http://127.0.0.1:8080/nar/gzip/954b3kw59mdvanp33yx93q5pzzll4wg9-qemu-5.0.0 
- 29605888
 qemu-5.0.0                                                           1.6MiB/s 
00:26 | 41.8MiB transferredBacktrace:
In ice-9/boot-9.scm:
  1731:15 19 (with-exception-handler #<procedure 7f485337bd50 at 
ice-9/boot-9.scm:1815:7 (exn)> _ # _ # …)
In guix/scripts/package.scm:
   966:10 18 (_)
In guix/status.scm:
    776:4 17 (call-with-status-report _ _)
In guix/store.scm:
   1300:8 16 (call-with-build-handler _ _)
   1300:8 15 (call-with-build-handler #<procedure 7f485337b000 at 
guix/ui.scm:1166:2 (continue store …> …)
In guix/scripts/package.scm:
    889:2 14 (_)
In guix/build/syscalls.scm:
   1167:4 13 (call-with-file-lock/no-wait _ _ _)
In guix/scripts/package.scm:
   143:19 12 (build-and-use-profile #<store-connection 256.99 7f4854803190> 
"/var/guix/profiles/per-u…" …)
In guix/store.scm:
  2042:24 11 (run-with-store #<store-connection 256.99 7f4854803190> _ 
#:guile-for-build _ #:system _ # …)
In guix/profiles.scm:
   1586:2 10 (_ _)
    348:2  9 (_ _)
In guix/store.scm:
  1924:12  8 (_ #<store-connection 256.99 7f4854803190>)
   1357:5  7 (map/accumulate-builds #<store-connection 256.99 7f4854803190> _ _)
  1368:15  6 (_ #<store-connection 256.99 7f4854803190> _ _)
   740:13  5 (process-stderr _ _)
In unknown file:
           4 (display "@ substituter-succeeded 
/gnu/store/277yzwcx6fshsxlqnwvyv94q66miv3ii-diffoscope…" …)
In guix/status.scm:
   699:16  3 (write! _ _ _)
    613:6  2 (_ (download-progress 
"/gnu/store/954b3kw59mdvanp33yx93q5pzzll4wg9-qemu-5.0.0" "http:…" …) …)
In guix/progress.scm:
   213:14  1 (display-download-progress "qem@" _ #:start-time _ #:transferred _ 
#:log-port _)
In ice-9/boot-9.scm:
  1669:16  0 (raise-exception _ #:continuable? _)

ice-9/boot-9.scm:1669:16: In procedure raise-exception:
In procedure =: Wrong type argument in position 1: #f

Maxim