Fix hiding keyboard animation stuck while dialog dismissing.

When dismissing a dialog with EditText focused and keyboard shown,
the keyboard does not get correctly dismissed.

This happens because after CL[1] landed, returning to the  activity won't start
new input connection, and the activity will thus not regain control over
the IME.

This fix restores the previous behavior, where  IMM will start a fake input
connection even without an editor.

[1]: I1ef3d341af9d473d94d52fd1890deafbae2bc9e1

Fix: 161273049
Test: atest CtsInputMethodTestCases
Test: manual as follows
     0) Have some files downloaded in the device
     1) Launch Files app > Browse > Click Internal Storage
     2) Long press on any file > From menu, click "Rename"
     3) Enter some name with soft keyboard and click "OK"
     4) Expect Keyboard should hide

Change-Id: I022ad658844142ff4a4cf3b91953013f2bfbb58a