Tie (debug build) crash

nightly 5062d11
0. My first score
1. "N"
2. "C"
3. "N"
4. "+"

Result: Crash

Discussion:
I think this happens because of https://github.com/musescore/MuseScore/blob/master/libmscore/utils.cpp#…
in Note* searchTieNote(Note* note)

Chord* c = toChord(seg->element(track));
if (c == 0 || !c->isChord())
continue;

We change the element to a chord before checking if it is valid.