Only mark unhandled events as handled when an action was made

The fix for b/304684672 was incomplete; while it would only
do an action when there was no modifiers, the event was still
marked as handled as it follow the same pattern as SysRQ;
however, in both cases, the event should not be marked as
handled if no action was made, so this CL will address it.

Bug: 304684672
Test: Flashed on device, confirmed Alt+Esc dispatches a fallback
when not handled

Change-Id: I9acf2c6c9daaabab16d9e4793fbd66a03beb7e6d