Allow users to open a new database even if one is already open

Since Open is a subclass of DatabaseCommand, it would previously be a
no-op if a database was already opened. This change causes the Open
command to reset the current database to nullptr before executing,
allowing a new database to be opened.

src/cli/Open.cpp

@@ -17,7 +17,7 @@
 
 #include "Open.h"
 
-#include <QtCore/QCommandLineParser>
+#include <QCommandLineParser>
 
 #include "DatabaseCommand.h"
 #include "TextStream.h"
@@ -29,6 +29,12 @@ Open::Open()
     description = QObject::tr("Open a database.");
 }
 
+int Open::execute(const QStringList& arguments)
+{
+    currentDatabase.reset(nullptr);
+    return this->DatabaseCommand::execute(arguments);
+}
+
 int Open::executeWithDatabase(QSharedPointer<Database> db, QSharedPointer<QCommandLineParser> parser)
 {
     Q_UNUSED(parser)

src/cli/Open.h

@@ -24,6 +24,7 @@ class Open : public DatabaseCommand
 {
 public:
     Open();
+    int execute(const QStringList& arguments) override;
     int executeWithDatabase(QSharedPointer<Database> db, QSharedPointer<QCommandLineParser> parser) override;
 };