Unterminated tie

[David Sumbler]

I have yet another problem related to repeats.  The piece I am setting
has one instrument which is tied from the last note in the
first-time-bar to the note at the start of the repeat.  (Moving the
repeats does not help, because there are a lot of overlapping ties.)

I tried to produce an unterminated tie in the last bar of the first
alternative by having a second, invisible voice with two tied notes in
the bar:

\version "2.19.24"

{ g'1 ~|
  \repeat volta 2 { g'1 | d'1 | }
  \alternative {
      {
          << { g'1 } \\ { \override Dots.stencil = ##f
                          \override Stem.stencil = ##f
                          \override Flag.stencil = ##f
                          g'2... ~ g'16
                          \revert Flag.stencil
                          \revert Stem.stencil
                          \revert Dots.stencil
                      } >> |
      } {
          a'1 |
      } }
  g'1 |
}

So far, so good, but the note heads in the bar are still there of
course.  But when I add "\override NoteHead.stencil = ##f" the compiler
gives up with the message:

Drawing systems...lilypond:
/home/gub/NewGub/gub/target/linux-64/src/lilypond-git.sv.gnu.org--lilypond.git-release-unstable/lily/skyline.cc:119:
void Building::precompute(Real, Real, Real, Real): Assertion `!isinf
(slope_) && !isnan (slope_)' failed.

Why does this happen?  And is there perhaps a simpler way of producing
my unterminated tie?