Fix bug #12957032 Stability-Sys: Java crash in com.android.settings:...

Fix bug #12957032 Stability-Sys: Java crash in com.android.settings: java.lang.NullPointerException:
...Attempt to invoke virtual method 'boolean android.os.Handler.sendEmptyMessage(int)' on a null object reference

- prevent NPE by checking the nullity of the Handler reference
- remove dead code
- rename mHandler to sHandler as it is a static

Change-Id: I7f4101f860f24b0cd49a4656971e9b54e55c1286