Backport of PR #7815, correct LDAP user count on setup with many users

(occ user:report)

LDAP: make sure cache key for paged result cookie matches when limit or offset is null or 0

LDAP: fix user report i.e. count for LDAP servers with really many users

initialize variable

var count is assigned in the inner loop so it must be checked inside there to be properly used as part of the exit condition of the outer loop

Put inner loop into own method, let's see whether it makes scrutinizer happier