Fix API host address in About dialog and debug message

The API server is listening on all interfaces. This is indicated by Qt
with the address 0.0.0.0 even if it is listening on both IPv4 and IPv6
https://doc.qt.io/qt-6/qhostaddress.html#toString
So the following addresses are valid
 http://127.0.0.1:8091/
 http://[::1]:8091/
 http://0.0.0.0:8091/
 http://[::]:8091/
plus any other address assigned to wired, wireless or virtual interfaces.

sdrbase/webapi/webapiserver.cpp

@@ -44,7 +44,7 @@ void WebAPIServer::start()
     if (!m_listener)
     {
         m_listener = new qtwebapp::HttpListener(m_settings, m_requestMapper, qApp);
-        qInfo("WebAPIServer::start: starting web API server at http://%s:%d", qPrintable(m_settings.host), m_settings.port);
+        qInfo("WebAPIServer::start: starting web API server at http://%s:%d", qPrintable(m_settings.host.isEmpty() ? "0.0.0.0" : m_settings.host), m_settings.port);
     }
 }
 
@@ -54,7 +54,7 @@ void WebAPIServer::stop()
     {
         delete m_listener;
         m_listener = 0;
-        qInfo("WebAPIServer::stop: stopped web API server at http://%s:%d", qPrintable(m_settings.host), m_settings.port);
+        qInfo("WebAPIServer::stop: stopped web API server at http://%s:%d", qPrintable(m_settings.host.isEmpty() ? "0.0.0.0" : m_settings.host), m_settings.port);
     }
 }
 

sdrgui/gui/aboutdialog.cpp

@@ -32,7 +32,7 @@ AboutDialog::AboutDialog(const QString& apiHost, int apiPort, const MainSettings
 	ui->dspBits->setText(QString("DSP Rx %1 bits Tx %2 bits").arg(SDR_RX_SAMP_SZ).arg(SDR_TX_SAMP_SZ));
 	ui->pid->setText(QString("PID: %1").arg(qApp->applicationPid()));
 	QString apiUrl = QString("http://%1:%2/").arg(apiHost).arg(apiPort);
-	ui->restApiUrl->setText(QString("REST API documentation: <a href=\"%1\">%2</a>").arg(apiUrl).arg(apiUrl));
+	ui->restApiUrl->setText(QString("REST API server and documentation: <a href=\"%1\">%2</a>").arg(apiUrl).arg(apiUrl));
 	ui->restApiUrl->setOpenExternalLinks(true);
 	ui->settingsFile->setText(QString("Settings: %1").arg(mainSettings.getFileLocation()));
 }

sdrgui/mainwindow.cpp

@@ -3096,7 +3096,7 @@ void MainWindow::loadDefaultPreset(const QString& pluginId, SerializableInterfac
 
 void MainWindow::on_action_About_triggered()
 {
-	AboutDialog dlg(m_apiHost.isEmpty() ? "127.0.0.1" : m_apiHost, m_apiPort, m_mainCore->m_settings, this);
+	AboutDialog dlg(m_apiHost.isEmpty() ? "0.0.0.0" : m_apiHost, m_apiPort, m_mainCore->m_settings, this);
 	dlg.exec();
 }