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: Ia018cac0910db7fc3be139ebdd65520d86742ba5
Signed-off-by: Roger Chen <cxr514033970@gmail.com>

Conflicts:
	src/com/android/mms/ui/MessageUtils.java