Mms: The subject will disappear after lock screen.

According to the above scene, the Activity invokes
onRestart(), and then load draft message.
It decides whether or not to display the subject
editText view according to the situation if there's
subject. As described above, there isn't any subject.

It decides whether or not to display the subject
editText view, according to the situation whether
there's subject or the editText view is visible before
leaving it. The second condition was added this time.

CRs-Fixed: BZ1089

Change-Id: I41d473c2558eda473531291f32fe73d0b7638e4f