Use index in SparseArray access properly

The original code was calling get() rather than valueAt(),
treating index as if it was a key.

Change-Id: I52539dfcb49b3d2ee3cb027d38c50b46f73b5ee7
Signed-off-by: Igor Chernyshev <igorc@google.com>
AudioService : Ensure uri is not null

Checks to make sure the uri is not null, otherwise the entire
subsystem crashes.

Change-Id: Iac04b6d11335236d527b8d5a1ccb48c1e09a4ac2