Call recording: catch exception on stop; fix member var naming

- when recording is stopped immediately after start, runtime exception
  is thrown to notify the app that the recording file should be deleted
  as it does not contain any useful data
- follow naming convention of member variables: use 'mRecorder' instead of
  'recorder'

Change-Id: I1c9d1752700b1d570a69774b54acd8ece03503da