Alarms: Fallback to defualt when uri is invalid

This fixes an issue where the media is no longer in the media store
but since the URI uses the "content" scheme it is deemed a valid
URI even though the media is no longer available. We check if the
content is actually available and if not we will fallback to the
default ringtone.

REF: BACON-1463

Change-Id: I7b77265dfbf410681a245b3b020d838f3d1c7eba
Automatic translation import

Change-Id: I6f24652794f1ecdebe2075c858ea1b10f9029c4f
Automatic translation import

Change-Id: Ie4056d5ad3112cfa35246031157a2642998e29ad
Merge branch 'cm-11.0' of https://github.com/CyanogenMod/android_packages_apps_DeskClock into android-4.4