MAP: Set Empty name or address for unknown values in GetMessageListing.

Set Empty sender or recipient name and address values to indicate
info not available from MSE in GetMessageListing response.
Current implemenation to skip the entire feild in response doesnot
mark the uniformity for values being fetched from telephony or
phone book databases.

Change-Id: I44e2f61572607349ec20ec1efcc6c44abe084b83