Error when deleting measures

[Whatang]

When multiple measures are deleted which make the number of measures in a line less, this can sometimes cause an error when the user tries to perform the next action.

In particular, find a line which ends with a section end or line break. Delete multiple measures from that line, not including the last measure on the line. Make sure that the last but one measure in the line is one of the ones deleted. Now try to add a note or right click on a measure line or measure anywhere on that line. An IndexError should be thrown.

[Whatang]

This seems to be something to do with the fact that the measure highlights are not being correctly updated when highlighted measures are deleted. After the deletion, DB thinks that the originally selected measures are still selected. When the user tries to perform the next action, the first thing that happens is that the selected measures are cancelled. Since measures were deleted this means that some of the NotePositions in the list of currently selected measures can be invalid. The selected measures should be cancelled before the delete is performed.