*BUG* cannot convert wide string to output locale

[jgart]

Hi Guixers!

I get the following backtrace when trying to upgrade nss-certs from 3.59 to 
3.71:

```
 λ guix upgrade nss-certs
The following package will be upgraded:
   nss-certs 3.59 → 3.71

0.1 MB will be downloaded
 nss-certs-3.71  128KiB                                                         
                                                                                
                         383KiB/s 00:00 [################# ]  99.6%Backtrace:
In guix/ui.scm:
   2229:7 19 (run-guix . _)
  2192:10 18 (run-guix-command _ . _)
In ice-9/boot-9.scm:
  1752:10 17 (with-exception-handler _ _ #:unwind? _ # _)
  1752:10 16 (with-exception-handler _ _ #:unwind? _ # _)
In guix/scripts/substitute.scm:
   771:15 15 (_)
    543:9 14 (process-substitution #<output: file 4> _ "/gnu/store/?" ?)
In guix/serialization.scm:
    424:4 13 (fold-archive _ _ _ _)
   468:33 12 (read "/gnu/store/l0axwdizcc12n0kdicwlm7lcds7ym40d-nss?" ?)
   468:33 11 (read "/gnu/store/l0axwdizcc12n0kdicwlm7lcds7ym40d-nss?" ?)
   468:33 10 (read "/gnu/store/l0axwdizcc12n0kdicwlm7lcds7ym40d-nss?" ?)
   468:33  9 (read "/gnu/store/l0axwdizcc12n0kdicwlm7lcds7ym40d-nss?" ?)
   451:26  8 (read "/gnu/store/l0axwdizcc12n0kdicwlm7lcds7ym40d-nss?" ?)
   520:22  7 (_ "/gnu/store/l0axwdizcc12n0kdicwlm7lcds7ym40d-nss-ce?" ?)
In ice-9/boot-9.scm:
  1747:15  6 (with-exception-handler #<procedure 7f787aabf6f0 at ic?> ?)
In unknown file:
           5 (symlink "NetLock_Arany_=Class_Gold=_F?tan?s?tv?ny.pem" #)
In ice-9/boot-9.scm:
  1685:16  4 (raise-exception _ #:continuable? _)
  1685:16  3 (raise-exception _ #:continuable? _)
  1780:13  2 (_ #<&compound-exception components: (#<&error> #<&orig?>)
  1685:16  1 (raise-exception _ #:continuable? _)
  1685:16  0 (raise-exception _ #:continuable? _)

ice-9/boot-9.scm:1685:16: In procedure raise-exception:
Throw to key `encoding-error' with args `("scm_to_stringn" "cannot convert wide 
string to output locale" 84 #f #f)'.
substitution of /gnu/store/l0axwdizcc12n0kdicwlm7lcds7ym40d-nss-certs-3.71 
failed
guix upgrade: error: some substitutes for the outputs of derivation 
`/gnu/store/l500rigm8inalbwyq42mxghv4zck4scm-nss-certs-3.71.drv' failed 
(usually happens due to networking issues); try `--fallback' to build 
derivation from source
```

Does anyone know what causes this one?

I was able to get around it by doing the following:

`guix upgrade nss-certs --no-substitutes`

`--fallback` as the backtrace suggested did not work for me.

all best,

jgart