bug#32929: `guix pull` fail

[Michael Bowcutt]

Hi, I ran into a bug.

after running `guix pull`:

```
Updating from Git repository at '
https://git.savannah.gnu.org/git/guix.git'...
Building from Git commit 9e783d0bf22a7ff965105eb45f6c179a832bbabf...
guile: warning: failed to install locale
Computing Guix derivation for 'x86_64-linux'... /Backtrace:
           9 (primitive-load "/gnu/store/2m09y8vajsla3zdlk28rcfdi3zq?")
In ice-9/eval.scm:
    155:9  8 (_ _)
    159:9  7 (_ #(#(#(#(#(#(#(#(#(#(#(?) ?) ?) ?) ?) ?) ?) ?) ?) ?) ?))
In ./guix/store.scm:
  1592:24  6 (run-with-store _ _ #:guile-for-build _ #:system _ # _)
In ./guix/self.scm:
   918:16  5 (_ _)
    492:4  4 (compiled-guix "/gnu/store/91a7if3r1h6x4y9vigzbw6y1rhi?"
?)
In srfi/srfi-1.scm:
   679:15  3 (append-map _ _ . _)
   592:17  2 (map1 (#f #<package address@hidden gnu/packa?> ?))
In ./guix/self.scm:
   494:31  1 (_ _)
In ./guix/packages.scm:
   743:21  0 (package-transitive-propagated-inputs #f)

./guix/packages.scm:743:21: In procedure package-transitive-propagated-
inputs:
In procedure struct_vtable: Wrong type argument in position 1
(expecting struct): #f
guix pull: error: You found a bug: the program
'/gnu/store/2m09y8vajsla3zdlk28rcfdi3zq7cvzq-compute-guix-derivation'
failed to compute the derivation for Guix (version:
"9e783d0bf22a7ff965105eb45f6c179a832bbabf"; system: "x86_64-linux";
host version: "0.15.0"; pull-version: 1).
Please report it by email to <address@hidden>.
```