HPCC-10802 Remove check for NULL user

Logging of NULL users is filling DALI logfiles, especially when security
is not enabled. This fix disables that logging

Signed-off-by: William Whitehead <william.whitehead@lexisnexis.com>
Merge pull request #5361 from RussWhitehead/nullUser

HPCC-10802 Remove check for NULL user

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>