Fix #1510

src/app/PortWidget.cpp

@@ -139,6 +139,9 @@ void PortWidget::onDragEnd(const event::DragEnd& e) {
 		return;
 
 	CableWidget* cw = APP->scene->rack->releaseIncompleteCable();
+	if (!cw)
+		return;
+
 	if (cw->isComplete()) {
 		APP->scene->rack->addCable(cw);
 

src/app/RackWidget.cpp

@@ -625,6 +625,9 @@ void RackWidget::setIncompleteCable(CableWidget* w) {
 }
 
 CableWidget* RackWidget::releaseIncompleteCable() {
+	if (!incompleteCable)
+		return NULL;
+
 	CableWidget* cw = incompleteCable;
 	cableContainer->removeChild(incompleteCable);
 	incompleteCable = NULL;