Clear the tree widget in the Structure tab when after closing a DB

Clear the tree widget in the 'Database Structure' tab of the main window
after closing a database.
See issue #44.

src/DbStructureModel.cpp

@@ -125,6 +125,13 @@ void DbStructureModel::reloadData(DBBrowserDB* db)
         rootItem->removeChild(rootItem->child(0));
     }
 
+    // Return here if no DB is opened
+    if(!db->isOpen())
+    {
+        endResetModel();
+        return;
+    }
+
     // Create the nodes for tables, indices, views and triggers
     QMap<QString, QTreeWidgetItem*> typeToParentItem;
     QTreeWidgetItem* itemTables = new QTreeWidgetItem(rootItem);

src/MainWindow.cpp

@@ -220,10 +220,15 @@ void MainWindow::populateStructure()
 {
     completerModelTables.clear();
     clearCompleterModelsFields();
+
+    // Refresh the structure tab
+    db.updateSchema();
+    dbStructureModel->reloadData(&db);
+    ui->dbTreeWidget->expandToDepth(0);
+
     if(!db.isOpen())
         return;
 
-    db.updateSchema();
     QStringList tblnames = db.getBrowsableObjectNames();
     sqliteHighlighterLogUser->setTableNames(tblnames);
     sqliteHighlighterLogApp->setTableNames(tblnames);
@@ -267,10 +272,6 @@ void MainWindow::populateStructure()
         sqlarea->getEditor()->setDefaultCompleterModel(&completerModelTables);
         sqlarea->getEditor()->insertFieldCompleterModels(completerModelsFields);
     }
-
-    // Refresh the structure tab
-    dbStructureModel->reloadData(&db);
-    ui->dbTreeWidget->expandToDepth(0);
 }
 
 void MainWindow::populateTable( const QString & tablename)

src/sqlitedb.cpp

@@ -757,10 +757,14 @@ void DBBrowserDB::updateSchema( )
     sqlite3_stmt *vm;
     const char *tail;
     int err=0;
+    lastErrorMessage = QObject::tr("no error");
 
     objMap.clear();
 
-    lastErrorMessage = QObject::tr("no error");
+    // Exit here is no DB is opened
+    if(!isOpen())
+        return;
+
     QString statement = "SELECT type, name, sql, tbl_name FROM sqlite_master;";
 
     QByteArray utf8Statement = statement.toUtf8();