bug#34778: Guix refresh -u fails

[Gábor Boskovits]

guix refresh -u unibilium
fails with the following backtrace:
address@hidden ~/guix$ ./pre-inst-env guix refresh -u unibilium
Backtrace:
          14 (apply-smob/1 #<catch-closure 728c20>)
In ice-9/boot-9.scm:
    705:2 13 (call-with-prompt _ _ #<procedure default-prompt-handle…>)
In ice-9/eval.scm:
    619:8 12 (_ #(#(#<directory (guile-user) 7ae140>)))
In guix/ui.scm:
  1654:12 11 (run-guix-command _ . _)
In ice-9/boot-9.scm:
    829:9 10 (catch _ _ #<procedure 7f7f2456b9b8 at guix/ui.scm:624…> …)
    829:9  9 (catch _ _ #<procedure 7f7f2456b9d0 at guix/ui.scm:750…> …)
In guix/scripts/refresh.scm:
    513:8  8 (_)
In guix/store.scm:
  1737:24  7 (run-with-store _ _ #:guile-for-build _ #:system _ # _)
In guix/scripts/refresh.scm:
   531:16  6 (_ _)
In srfi/srfi-1.scm:
    640:9  5 (for-each #<procedure 289bd20 at guix/scripts/refresh.…> …)
In guix/scripts/refresh.scm:
   301:20  4 (update-package #<store-connection 256.99 93be10> #<pa…> …)
In guix/upstream.scm:
   374:22  3 (package-update #<store-connection 256.99 93be10> _ _ # _)
   302:17  2 (download-tarball #<store-connection 256.99 93be10> #f # …)
In guix/download.scm:
   568:55  1 (download-to-store #<store-connection 256.99 93be10> #f …)
In unknown file:
           0 (basename #f #<undefined>)

ERROR: In procedure basename:
In procedure scm_to_utf8_stringn: Wrong type argument in position 1
(expecting string): #f

guix describe output:
address@hidden ~/guix$ guix describe
41 generáció    márc 04 2019 11:53:03    (jelenlegi)
  guix 3499638
    repository URL: https://git.savannah.gnu.org/git/guix.git
    branch: master
    commit: 3499638ef87191d458f3e07455a9a0fefe76c085

guix refresh unibilium works just fine.