Bug 5415 More consistent returns from SimpleSearch

Bug 5415 More consistent returns from SimpleSearch

SimpleSearch returns a 3 element array the first pf which is an error
indication. If an error is returned the other elements are
undefined. If error is undef the other elements are defined
This restores the consistency of the interface as it was before
the addition of zebra

Signed-off-by: Christophe Croullebois <christophe.croullebois@biblibre.com>
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>