Silence uninit var warnings from query normalizer

$field_info can return undef from the search for a matching ID from the
list of normalizers, which in turn generates several uninit var warnings
when attempts are made to access members of the undef variable. We saw
6700 occurrences of these warnings during a typical day of operations.

Signed-off-by: Dan Scott <dscott@laurentian.ca>
Signed-off-by: Bill Erickson <berick@esilibrary.com>