Crash on exit in ~ScoreView()

KUbuntu 13.04, commit 6bc6742.

Steps to reproduce:
1. Open MuseScore, enable ALSA or JACK MIDI driver. Close MuseScore.
2. Open MuseScore.
3. Open some score.
4. Close MuseScore.

Expected behaviour: MuseScore just closes.
Actual behaviour: MuseScore crashes in ~ScoreView() when tries to call seq->recomputeMaxMidiOutPort().