Raw content of script is shown instead of POD

[ikedas]

• On Debian (at least Debian 11 bullseye, afaik), if perl has been installed but perl-doc package which includes perldoc has not, /usr/bin/perldoc is replaced with a placeholder as below:

  #!/bin/sh
  # place-holder, diverted by perl-doc
  echo You need to install the perl-doc package to use this program. >&2
  exit 1
  

• On the other hand, Pod::Usage uses perldoc by default to format POD in the script.
  However, if perldoc returns non-zero exit status, Pod::Usage try to fallback to the pager.

As a result, raw content of the script is shown instead of POD section.