Fix missing CEA-708 closed captions.

Recently NBC has changed their CEA-708 encoding and exposed a MythTV
bug.  When the caption window is resized to be smaller, MythTV
inappropriately clears the buffer before an existing caption has been
displayed.  This makes it appear as though many/most captions are
lost.  This patch corrects that (and also makes CEA-608 log output
more readable).