Lyric extender extends far beyond end of voice

[David Feuer]

This is a problem when an extra voice ends on a long note or series of notes.

Short example:

\version "2.11.19"
\include "english.ly"

melody = \relative c' {
 a4 b c d |
 \voiceOne
 <<
   { e f g a | c d c d | }
   \new Voice = extra {
     \voiceTwo
     f, g a b ~ |
     b ~ b ~ b ~ b |
   }
 >>
 \oneVoice
 a b c d |
}

words = \lyricmode {
 one two three four
 five six seven eight
 nine ten eleven twelve
}

extrawords = \lyricmode {
 uno dos tres cuatro __
}

<<
 \new Voice = mel \melody
 \new Lyrics \lyricsto mel \words
 \new Lyrics \lyricsto extra \extrawords
> >