Fix NullPointerException reported through market.

If user selects the oldest build our changelog won't have a begin point
so we assume user is asking about since the begining of time (UnixTime=0)

PS2: Catch and log possible NullPointers from the market
	ChangelogFragment.onClickSave -> NullPointerException

PS3: Form url if shorturl is not provided

Change-Id: I5f2ab7e78a72dca756005127e8d944c68d1f6607