fix error introduced in a previous commit

fix error introduced in a previous commit

Change to GetReservesFromBiblionumber() had effect
of causing all requests of constrainttype other
than 'o' to not be included in result.

while ($foo) {
    $bar or next;
    # do stuff
    # do other stuff
}

is not equivalent to

while ($foo) {
    if ($bar) {
        # do stuff
    }
    # do other stuff

}

Signed-off-by: Galen Charlton <galen.charlton@liblime.com>
Signed-off-by: Henri-Damien LAURENT <henridamien.laurent@biblibre.com>