Check whether mimetype is empty or not

Contacts Provider throws illegal argument Exception if
Mimetype of any data kind is empty. Contacts application does not have
any check for mimetype being empty when contacts get saved.

Check whether mimetype is empty or not before saving a contact.

Change-Id: Ibf9da0fd7f8665e571150e40109a6f3da26b8cbe
CRs-Fixed: 546239