Correct the comparision used so that lower/upper bounds work

The comparision function did not work properly.  Give it the length
of the expected key, and do not require the a specific input to the
comparision to be the search key.

This had caused issues where the key was not in the expected argument,
allowing strings that were shorter than the key length to be selected
as output.
3 jobs for fix_search in 11 minutes and 18 seconds
Status Job ID Name Coverage
  Build And Test
passed #246381
ligo-channel-completion:buster

00:01:15

passed #246383
ligo-channel-completion:jessie

00:11:18

passed #246382
ligo-channel-completion:stretch

00:01:07