SSA: Fix duplication of \ as the last character in lines
SSA: Fix duplication of \ as the last character in lines

Probably a regression.
Fixes Binchou_march.mkv.

Fixes #607

MaddTheSane/perian,MaddTheSane/perian,MaddTheSane/perian,MaddTheSane/perian,MaddTheSane/perian,MaddTheSane/perian