fix #29, you can`t move selected blocks in place which causes bus segment deletion

libs/blockview/blockbusitem.cpp

@@ -304,6 +304,14 @@ void BlockBusItem::simplify(bool full) {
 }
 
 
+bool BlockBusItem::hasNullSegment() const {
+	for (int s = 0; s < segments.size(); ++s) {
+		if (pol[segments[s].first] == pol[segments[s].second]) return true;
+	}
+	return false;
+}
+
+
 void BlockBusItem::adjustLine() {}