nested \fill-lines misalign

[Rune Zedeler]

The two "|FOO|"s are misaligned.

\version "2.10.1"
\header
{
  title = \markup \column {
    \fill-line { "|FOO|" }
    \fill-line { \fill-line { "|FOO|" } }
  }
}
\score {c''}