Correct attachment type for Mms only has subject

Mark the attachment type of Mms only has subject as TEXT
avoid to show Mms View as untimely

Change-Id: I346ae4af4983e9e8dbe9533eeddef445affc339a
Signed-off-by: Roger Chen <cxr514033970@gmail.com>
Check if mmp's encoded subject is null before used

Change-Id: I1de3c83b2b68128f725f8bbaf3d6764b2bdf836b
Signed-off-by: Roger Chen <cxr514033970@gmail.com>