bug 3219: handle variation in Amazon responses

bug 3219: handle variation in Amazon responses

An Amazon ItemLookup response can sometimes have
more than one Item element, where the ones after
the first appear to be cross references to items
that have the same ISBN.  Changed parsing so that
those responses are no longer treated like pseudohashes.

This fixes the following crash:

[error] detail.pl: Pseudo-hashes are deprecated at /catalogue/detail.pl line
213., referer: /cgi-bin/koha/catalogue/detail.pl

Which may lead to a nasty:
[error] Out of memory!, referer: /cgi-bin/koha/catalogue/detail.pl

Signed-off-by: Galen Charlton <galen.charlton@liblime.com>