Fix bug -> Click more than 2 cards within 500ms waiting will cause problem.

[suyangzuo]

In the original version, Due to checkForMatch will run after 500ms delay, so if click more than 2 cards within 500ms, the cardsChosen.length will longer than 2.

And, the checkForMatch will run only on condition cardsChosen.length === 2, so cardsChosen[2], cardsChosen[3] maybe after will not trigger checkForMatch.

This commit move the cardsChosen = [] and cardsChosenId = [] out of checkForMatch and put them into flipCard before checkForMatch runs, and use copy to replace them in checkForMatch.