multimedia/get_iplayer: Fix rc.d script and typo in pkg-message

The latest version of get_iplayer (ports r541176) introduced the following code:

export HOME="$get_iplayer_chdir"
cd "$HOME" || exit 1

This is always executed irrespective of rcvar get_iplayer_enable. The default
homedir for the get_iplayer user is /nonexistent. Therefore, upon each boot,
the script would emit the following error:

cd: /nonexistent: No such file or directory

with no indication of the source of the error.

PR: 251987
Submitted by: Jamie Landeg-Jones <jamie@catflap.org> (maintainer)
Reported by: Niels Bakker <niels=freebsd@bakker.net>
MFH: 2021Q1