Cancel TST's default action for mouseup when the action is overridden

I got a bug report https://github.com/piroor/treestyletab/issues/2127 and I've realized that tst-tabflip doesn't cancel TST's default action even if it is overridden by tst-tabflip. Old versions of TST worked as expected but it was just a luck, and originally TST's default behavior need to be canceled in this case. Could you merge this?