Stability improvement

[excln]

• The application sometimes crashes when opening another bmson, previewing a sound channels, editing events, or undo/redoing.

[excln]

A significant bug was fixed in c8d2b56 that had been making many crashes when scrolling sequence view on 64bit platforms.

[djkero]

* The application sometimes crashes when opening another bmson, previewing a sound channels, editing events, or undo/redoing.

Have any clue about the root of these issues? Could you make one issue per bug so we can investigate and fix them, and if you have the time, help with it?