Bug 8175 - check logs error or displays incorrectly in details.pl

Bug 8175 - check logs error or displays incorrectly in details.pl

Changed "$item->{'materials'} ne ''" to
"defined($item->{'materials'}) && $item->{'materials'} =~ /\S/"
in if condition to prevent error when it is NULL, and to
properly capture the intent of printing if there is something
visible.

Cases tested include NULL, '0', '', ' ', and 'blah' by using
 UPDATE items SET materials=NULL where biblionumber=19158;
where the biblionumber was chosen randomly, because only NULL
was in the items.materials field. The NULL case triggers an
error, but it does display correctly.

The ' ' case displays an apparently empty column, which does not
seem to be the intent of the flag that is being set. This is why
a simple $var check is not sufficient.

Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>