Tie_engraver doesn't handle TrillPitchGroup collisions

[Valentin Villenave]

Hi everybody,

here's my daily bug report :)

In the following snippet, the tie is overlapping the TrillPitchHead
(it's not a major bug, but as trilled notes are often tied, it can
still be annoying)

\relative {
\pitchedTrill a''1~\startTrillSpan c
a\stopTrillSpan
}

Regards,
Valentin