Issue 4130: Isolated durations don't work after \pageBreak

Issue 4130: Isolated durations don't work after \pageBreak

The example
\score {
  \new RhythmicStaff {
    R1 |
    \pageBreak
    1~ |
    8 r r4 r2 |
  }
}

led to unexpected results since \pageBreak produces an EventChord which
is then taken as a repeat note by 1~.  This patch makes sure that
repeated durations only attach to event chords containing rhythmic
events.