Suppress remove null widget warning

And improve text format for translation work.

src/gui/properties/propertieswidget.cpp

@@ -752,21 +752,31 @@ void PropertiesWidget::configure()
     // Speed widget
     if (Preferences::instance()->isSpeedWidgetEnabled())
     {
-        if (!m_speedWidget || !qobject_cast<SpeedWidget *>(m_speedWidget))
+        if (!qobject_cast<SpeedWidget *>(m_speedWidget))
         {
-            m_ui->speedLayout->removeWidget(m_speedWidget);
-            delete m_speedWidget;
-            m_speedWidget = new SpeedWidget {this};
+            if (m_speedWidget)
+            {
+                m_ui->speedLayout->removeWidget(m_speedWidget);
+                delete m_speedWidget;
+            }
+
+            m_speedWidget = new SpeedWidget(this);
             m_ui->speedLayout->addWidget(m_speedWidget);
         }
     }
     else
     {
-        if (!m_speedWidget || !qobject_cast<QLabel *>(m_speedWidget))
+        if (!qobject_cast<QLabel *>(m_speedWidget))
         {
-            m_ui->speedLayout->removeWidget(m_speedWidget);
-            delete m_speedWidget;
-            auto *label = new QLabel(tr("<center><b>Speed graphs are disabled</b><p>You may change this setting in Advanced Options </center>"), this);
+            if (m_speedWidget)
+            {
+                m_ui->speedLayout->removeWidget(m_speedWidget);
+                delete m_speedWidget;
+            }
+
+            const auto displayText = QString::fromLatin1("<center><b>%1</b><p>%2</p></center>")
+                .arg(tr("Speed graphs are disabled"), tr("You can enable it in Advanced Options"));
+            auto *label = new QLabel(displayText, this);
             label->setAlignment(Qt::AlignHCenter | Qt::AlignVCenter);
             m_speedWidget = label;
             m_ui->speedLayout->addWidget(m_speedWidget);