Ensure correct TCOs after cloning tracks into the BB editor

Previously BBTrackContainerView::dropEvent always deleted
the TCOs of dropped tracks. It made dropped tracks unusable.
As of this commit, the function checks for correct TCOs.
If incorrect TCOs exist, the function remove them and add empty ones.

src/gui/editors/BBEditor.cpp

@@ -258,7 +258,25 @@ void BBTrackContainerView::dropEvent(QDropEvent* de)
 		DataFile dataFile( value.toUtf8() );
 		Track * t = Track::create( dataFile.content().firstChild().toElement(), model() );
 
-		t->deleteTCOs();
+		// Ensure BB TCOs exist
+		bool hasValidBBTCOs = false;
+		if (t->getTCOs().size() == m_bbtc->numOfBBs())
+		{
+			hasValidBBTCOs = true;
+			for (int i = 0; i < t->getTCOs().size(); ++i)
+			{
+				if (t->getTCOs()[i]->startPosition() != MidiTime(i, 0))
+				{
+					hasValidBBTCOs = false;
+					break;
+				}
+			}
+		}
+		if (!hasValidBBTCOs)
+		{
+			t->deleteTCOs();
+			t->createTCOsForBB(m_bbtc->numOfBBs() - 1);
+		}
 		m_bbtc->updateAfterTrackAdd();
 
 		de->accept();