Fixed -list option to otrs.CheckModules.pl

The CheckModules script has a -list option in the master branch that generates a list of packages to install, This can save lots of time when doing a manual installation.

However, it currently generates an error message. This PR fixes that error message.
```
Copyright (C) 2001-2014 OTRS AG, http://otrs.com/
usage: otrs.CheckModules.pl [-list|all]

   otrs.CheckModules.pl
       Returns all required and optional packages of OTRS.

   otrs.CheckModules.pl -list
       Returns a install command with all required packages.

   otrs.CheckModules.pl -all
       Returns all required, optional and bundled packages of OTRS.


$ bin/otrs.CheckModules.pl -list
Undefined subroutine &main::IsArrayRefWithData called at bin/otrs.CheckModules.pl line 504.
```