Fix the base note automation fix (#6828)

Towards the end of the development for the fix of #6548 (via #6725) the upgrade code was refactored into its own class. While doing so it was forgotten to actually call the `upgrade` method on the `UpgradeExtendedNoteRange` instance. As a result almost all files should currently open in a wrong state with many instruments transposed. This commit fixes this.

Also explicitly check the assertion that BB tracks do not contain other BB tracks.

src/core/DataFile.cpp

@@ -1671,6 +1671,8 @@ void DataFile::upgrade_extendedNoteRange()
 {
 	auto root = documentElement();
 	UpgradeExtendedNoteRange upgradeExtendedNoteRange(root);
+
+	upgradeExtendedNoteRange.upgrade();
 }