after failed loading from XML, don't add empty item (#997)

GUI/View/View/InstrumentView.cpp

@@ -106,8 +106,10 @@ void InstrumentView::createActions(QToolBar* toolbar)
     m_load_action->setIcon(QIcon(":/images/library.svg"));
     m_load_action->setToolTip("Load an instrument from the instrument library");
     toolbar->addAction(m_load_action);
-    connect(m_load_action, &QAction::triggered,
-            [this] { m_set->add_item(IO::loadComponentFromXML<InstrumentItem>("instrument")); });
+    connect(m_load_action, &QAction::triggered, [this] {
+        if (InstrumentItem* t = IO::loadComponentFromXML<InstrumentItem>("instrument"))
+            m_set->add_item(t);
+    });
 
     //... Actions on selected instrument