enrich log message with backtrace, but level it down to DEBUG
enrich log message with backtrace, but level it down to DEBUG

The message is not helpful anyway for an admin, and oftentimes is just
valid (e.g. when searching with an offset beyond users in LDAP).

Signed-off-by: Arthur Schiwon <9ae9918f3cbf5a90ebc25affe594cc53853aee42@arthur-schiwon.de>

andreas-p/nextcloud-server,andreas-p/nextcloud-server,nextcloud/server,michaelletzgus/nextcloud-server,michaelletzgus/nextcloud-server,nextcloud/server,michaelletzgus/nextcloud-server,andreas-p/nextcloud-server,andreas-p/nextcloud-server,nextcloud/server,michaelletzgus/nextcloud-server,andreas-p/nextcloud-server,nextcloud/server