Dont finish handwriting inking was prepared for session

If handwriting is started on unfocused view, startInput and hence
finishInput would be called. If IME prepared handwriting inkWindow for
the session, dontattempt to finish handwriting.
This should help with improving latency on unfocused editors

Bug: 287109569
Test: atest StylusHandwritingTest
Change-Id: I28c206dd5ca1aafb257f6050379c159190ab3d60