Ignore broken input channel when finishing input event.

There are occasional races during application shut down where the
input dispatcher will close an input channel before the application
has finished its last event.  So just ignore EPIPE.

Also tweak the logging for failed input event injection to make
it clearer which pid was trying to perform the injection.

Bug: 6013004
Change-Id: I7bbb01441d41762b03eafd4d39dcf0323e1cadf3