PreferenceActivity should not leave message in looper when destroyed

When a PreferenceActivity is destroyed as soon as created,
there is a problematic case that messages for the activity are
sometimes left in the looper even after the activity is destroyed.
For example, by clearing user data of the selecting IME on
Settings apk, com.android.settings.Settings is re-launched
2 times successively. (Destory->Create->Destroy->Create)
Due to the left message, application crash can happen.
(NullPointerException at BackStackRecord.getBreadCrumbTitle())

Two cases have been found to observe this issue.
[Case 1]
 1,Launch IME in advance.
 2,Go to Settings >Apps > All and choose the IME package.
 3,Click "Clear data"
 4,Application crash occurs on com.android.settings.
[Case 2]
 1,Go to Settings > Language&input > Language.
 2,ListView dialog to choose language is shown.
 3,Rotate the tablet 180 degree so that 90 degree rotation occurs twice.
 4,Application crash occurs on com.android.settings.

Change-Id: I5ce36ea7a40ab7bc7737b7dca6641a4c3d77a480