Prevent crash when menu item is selected to early.

pglab/DatabaseWindow.cpp

@@ -261,6 +261,9 @@ void DatabaseWindow::newCrudPage(Oid tableoid)
 
 void DatabaseWindow::newCatalogInspectorPage(QString caption, NamespaceFilter filter)
 {
+    if (!m_database)
+        return; // would be better if we queued the operation for later
+
 	auto ct = new CatalogInspector(m_database, this);
 	ct->addAction(actionRefreshCatalog);