Fix Change Events triggering on Init (#102)

[guidocatalusci]

Hi,
thank you very much for this plugin, it's Amazing!

I've found that the change event is triggered when the plugin is initialised.
The problem was on line 587, where you've made a conditional statement where you check if the previous variable is Null, but the variable is Undefined.
I've also changed the OR condition to AND.

Let me know if that helped.

---

Line 586:
if (previous !== null && previous !== undefined &&
i.selectedTime !== null && i.selectedTime !== undefined) {
i.element.trigger('time-change', [time]);
if ($.isFunction(i.options.change)) {
i.options.change.apply(i.element, [time]);
}
}

[berkaygure]

I have the same problem. I have 10 inputs and it triggers for each of them on initialize phase. Also, it overrides my onClick handlers.

@wvega I really appreciate it if you would merge it.