fix(xmlwf): try _parse_help before _parse_usage

Recent versions of xmlwf no longer output a parseable usage formatted
blurb at the top. And at least as of xmlwf from expat 2.2.9, even if it
still does, parsing it as help yields better options coverage.

Fixes related test on current Alpine.

$ xmlwf -v
xmlwf using expat_2.2.9
[...]
$ xmlwf --help
usage: xmlwf [-s] [-n] [-p] [-x] [-e ENCODING] [-w] [-r] [-d DIRECTORY]
             [-c | -m | -t] [-N]
             [FILE [FILE ...]]
[...]

$ xmlwf -v
xmlwf using expat_2.4.1
[...]
$ xmlwf --help
usage:
  xmlwf [OPTIONS] [FILE ...]
  xmlwf -h
  xmlwf -v
[...]

Author: scop

completions/xmlwf

@@ -21,7 +21,9 @@ _xmlwf()
     esac
 
     if [[ $cur == -* ]]; then
-        COMPREPLY=($(compgen -W '$(_parse_usage "$1")' -- "$cur"))
+        COMPREPLY=($(
+            compgen -W '$(_parse_help "$1" || _parse_usage "$1")' -- "$cur"
+        ))
         return
     fi