TargetSetupPage: Use old importer to clean up when switching

Use the old importer when cleaning while switching to a new importer.

Change-Id: I8fd3af32271b839502571ee3806903abd927ef0a
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/plugins/projectexplorer/targetsetuppage.cpp

@@ -302,10 +302,11 @@ void TargetSetupPage::setProjectImporter(ProjectImporter *importer)
     if (importer == m_importer)
         return;
 
+    reset(); // Reset before changing the importer!
+
     m_importer = importer;
     m_importWidget->setVisible(m_importer);
 
-    reset();
     setupWidgets();
 }