(hexl-insert-multibyte-char): Avoid using `string-as-unibyte'

* lisp/hexl.el (hexl-insert-multibyte-char): Avoid using
`string-as-unibyte' in the fallback case.
1 job for master in 57 minutes and 32 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
failed #1806
test-all

00:57:32

 
Name Stage Failure
failed
test-all Test
make[2]: *** [check-doit] Error 1
Makefile:318: recipe for target 'check-doit' failed
make[2]: Leaving directory '/builds/emacs/emacs/test'
make[1]: *** [check-expensive] Error 2
Makefile:293: recipe for target 'check-expensive' failed
make[1]: Leaving directory '/builds/emacs/emacs/test'
Makefile:957: recipe for target 'check-expensive' failed
make: *** [check-expensive] Error 2
ERROR: Job failed: exit code 1