Defect 1: ValidateLdap used AddIfNotPositive for Port, accepting any value
> 0 including 70000. Replaced with builder.Port() from the shared
ZB.MOM.WW.Configuration library, which enforces the 1-65535 TCP range and
emits "MxGateway:Ldap:Port must be between 1 and 65535 (was {value})".
Defect 2: AddIfInvalidPath only caught ArgumentException, NotSupportedException,
and PathTooLongException from Path.GetFullPath. On macOS/Linux a path containing
an embedded null throws IOException, which escaped the catch block and caused
Validate() to throw instead of returning a failure. Added catch (IOException).
Tests: added Validate_Fails_WhenLdapPortIsZero, Validate_Fails_WhenLdapPortExceedsMaximum,
and Validate_Succeeds_WhenLdapEnabledWithValidPort to cover the new range boundary.
Joseph Doherty