simplify parenting with main window

GUI/Views/ImportDataWidgets/LinkInstrumentManager.cpp

@@ -57,15 +57,14 @@ bool LinkInstrumentManager::canLinkDataToInstrument(const RealDataItem* realData
         GUI::View::ImportDataUtils::Compatible(*instrumentItem, *realDataItem);
     if (!isCompatible) {
         if (!quiet)
-            QMessageBox::warning(MainWindow::instance(), "Can't link to instrument",
+            QMessageBox::warning(baWin, "Can't link to instrument",
                                  "Can't link, data is incompatible with the instrument.");
         return false;
     }
 
     if (realDataItem->isSpecularData() && !realDataItem->hasNativeData()) {
         if (!quiet)
-            QMessageBox::warning(MainWindow::instance(), "Can't link to instrument",
-                                 "Can't link, data is empty.");
+            QMessageBox::warning(baWin, "Can't link to instrument", "Can't link, data is empty.");
         return false;
     }
 

GUI/mainwindow/mainwindow.h

@@ -111,4 +111,6 @@ private:
     static MainWindow* s_instance;
 };
 
+#define baWin (MainWindow::instance())
+
 #endif // BORNAGAIN_GUI_MAINWINDOW_MAINWINDOW_H