Check if mmp's encoded subject is null before used

From AOSP:
  https://android-review.googlesource.com/#/c/57709/1

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

Patch set 2 : correction
Patch set 3 : correction
Patch set 4 : correction

Change-Id: I9cbfc102b8bc1dd9b165a5097df2e614106bd385
Merge branch 'cm-10.1' of github.com:CyanogenMod/android_packages_apps_Mms into cm-10.1