HPCC-9106 Incorrect determination of password expiration prompt

The test for whether or not to set passwordDaysRemaining to -1 incorrectly
casts passwordDaysRemaining to an unsigned. This is incorrect, because it
can be negative (-1 means expired, -2 means never expires). This fix corrects
the problem by treating it as an integer

Signed-off-by: William Whitehead <william.whitehead@lexisnexis.com>
Merge pull request #4226 from RussWhitehead/isPwdExp

HPCC-9106 Incorrect determination of password expiration prompt

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>