According to the Simple Identity Management Profile (DSP1034)
document the LMI_Account.UserPassword property should not contain
the password itself, no matter how encrypted it is. It should either
contain an array of zero elements when password has been set or
NULL when password is missing or not configured.

Another change this commit brings is a more precise behaviour
of LMI_Account.ModifyInstance() method. When the UserPassword
property is array of zero elements, no change regarding password
is made. This case was previously treated as a request for password
removal. The DSP1034 profile doesn't specify such scenario, let's
treat it the same way as the GetInstance() operation.