Fix checks for showing InputMethod picker

When user tries to switch IME, IMMS.showInputMethodPickerFromClient()
is called. The call fails to validate in newly introduced
canShowInputMethodPickerLocked() in
I4f0fc21268200c64d12b31ca54416acfbf62f37b because
mCurClient.client != client.

This is happening since the new client never started input ever since
we prevented calls to startInputUncheckedLocked in
Ibf9dab3d9c138b5f04e053d41ee4fd248c78e4da.

The fix is to update mCurFocusedWindowClient.client instead of
mCurclient.client in canShowInputMethodPickerLocked()

Fixes: 72557082
Test: manually using the steps in bug
Test: atest InputMethodManagerTest
Change-Id: I4e21625c32a0ca1abc740229efb3c7fcd97141cc