Fix null pointer dereference when security exception occurs

Just above the SecurityException is a check for r.record == null,
thus dereferencing r.record will cause a null pointer exception.

Found in Android 4.3 with the following steps:

1) Start the music app.
2) Switch to the restricted user.
3) Navigate to Settings->Apps->Running->Music.
4) Tap the stop button.

The security exception should be thrown which results in
a nice message to the user, but instead a null pointer
exception is thrown which results in the settings app
crashing.

Change-Id: I4a306c38650c9d366896e592767dde70adb71c57