Initialize broadcastTimer to null and check if timer is null before…

[azanli]

…attempting to invoke cancel()

Patch in reference to #36

The only difference is that broadcastTimer is initialized to null value since that is what it becomes after broadcastTimer.cancel(), so that it can be checked against that value, i.e. broadcastTimer != null before invoking broadcastTimer.cancel(). `

[alexkendall]

Looks good.