Restore TimePickerDialog#onClick behavior.

onClick used to dismiss the dialog recording the set time.
In ag/1831151 I removed handling of BUTTON_POSITIVE as the button
clicks were now handled via click listener set in show(). However,
onClick can be also called programatically and not just via clicking
the button. This CL restores that behavior. It will skip validation
and use the last valid hour and minute.

Bug: 36037351
Test: TimePickerDialogTest#testOnClick now passes
Change-Id: I15952dadab0c7b73ae5fecb1539edf5ebddec68c