Update internal states stored in InputMethodManager properly

Bug: 4517456

"startInputInner" in InputMethodManager.java will call "startInput" in InputMethodManagerService.java
In startInputLocked in IMMS, mCurSeq (Bind sequence) is incremented, but if mCurMethod stored in
InputMethodManager.java is not null, mBindSequence in InputMethodManager.java will not be updated
to the incremented sequence.

Hence, after this procedure, unbinding IME will be cancelled by the mismatch of the bind sequence.

This situation happens when user changes the focused text view.
If I remember correctly, some behaviors of showing or hiding IME at switching text view were changed.
And I think this bug appeared because of that change.

Change-Id: Icec380f3ca05cf798cc4b82155d0cecf178633a5