Don't try to prune SSA style spans if there's only one of them. (fixes crash on 0-byte subtitle lines)
Don't try to prune SSA style spans if there's only one of them. (fixes crash on 0-byte subtitle lines)

MaddTheSane/perian,JanX2/Perian,MaddTheSane/perian,JanX2/Perian,JanX2/Perian,JanX2/Perian,MaddTheSane/perian,JanX2/Perian,MaddTheSane/perian,MaddTheSane/perian,MaddTheSane/perian