Bug 18355: (QA follow-up) Rearrange comments, improve code

Bug 18355: (QA follow-up) Rearrange comments, improve code

Comments were hard to read (for me) but tastes differ..

Code should reflect that permanent_location is a code and that location
may be already an authval. See detail.pl:
$item->{'location'} = $shelflocations->{$shelfcode} if ( defined( $shelfcode ) && defined($shelflocations) && exists( $shelflocations->{$shelfcode} ) );

Obviously, this kind of logic divided over two places should be reduced.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>