remove unnecessary condition which blocks gc

[viclm]

The code above has removed the event handler, so the condition is not necessary.

The off() hammerjs provide has a bug that it does not remove the event key on handlers object unless calling it without the second argument, so there will be a blank array left if you remove the last handler by calling the off() with a second argument.

In this context, the handlers will contains a tap key with a value of [], you should cover it if the condition is really necessary.