shellcheck: asciidoc-helper.sh issues

In doc/asciidoc-helper.sh line 22:
      TZ=UTC "$2" -d manpage -o $output $input;
                                ^-----^ SC2086: Double quote to prevent globbing and word splitting.
                                        ^----^ SC2086: Double quote to prevent globbing and word splitting.


In doc/asciidoc-helper.sh line 47:
    if "$2" -f manpage $input; then
                       ^----^ SC2086: Double quote to prevent globbing and word splitting.


In doc/asciidoc-helper.sh line 48:
      mv $base.1 $output;
         ^---^ SC2086: Double quote to prevent globbing and word splitting.
                 ^-----^ SC2086: Double quote to prevent globbing and word splitting.

For more information:
  https://www.shellcheck.net/wiki/SC2086 -- Double quote to prevent globbing ...