Fix cilineendings_unittest +style issues

- Wrapped lines in cilineendings_unittest.cpp to 80 columns
- Renamed test file with capital 'I' in filename, so it is lower cased.
- Make use of helper functions for error checks where possible
- Expect rather than assert where possible
- Safety checks to prevent buffer overflows/out of bounds access
- Code corrected so that 'self->column' is reset to '1' each time  webvtt_proc_cueline is called