Fix: Sticky keys filter should ignore incomplete key events

When sticky keys filter is enabled while some keys are pressed
down on the keyboard, the key up on those keys should not affect
the sticky state.

Bug: 381239751
Test: atest --host libinputflinger_rs_test
Flag: EXEMPT bugfix
Change-Id: I3142883f33e9783b7ca09c3291f75b4008f6a13f