Remove skip newline logic from read_cuetext.

Since we are reading in the newline character in string_getline we no longer
need to skip the newline character after the fact.
Fix escape tokenizer to end on correct status.

When the escape tokenizer has parsed an escape character sequence properly
or it has found a character that cannot belong to an escape sequency it
should switch it's status to WEBVTT_UNFINISHED so the cue text tokenizer
knows that it is not finished.