Fix calling methods on null objects

Some object methods were calling without checking if the object
exist or not.

src/mainwindow.cpp

@@ -2018,26 +2018,27 @@ void MainWindow::slotRenderProject()
 {
     KdenliveDoc *project = pCore->currentDoc();
 
-    if (!m_renderWidget) {
-        if (project) {
-            m_renderWidget = new RenderWidget(project->useProxy(), this);
-            connect(m_renderWidget, &RenderWidget::shutdown, this, &MainWindow::slotShutdown);
-            connect(m_renderWidget, &RenderWidget::selectedRenderProfile, this, &MainWindow::slotSetDocumentRenderProfile);
-            connect(m_renderWidget, &RenderWidget::abortProcess, this, &MainWindow::abortRenderJob);
-            connect(m_renderWidget, &RenderWidget::openDvdWizard, this, &MainWindow::slotDvdWizard);
-            connect(this, &MainWindow::updateRenderWidgetProfile, m_renderWidget, &RenderWidget::adjustViewToProfile);
-            m_renderWidget->setGuides(project->getGuideModel());
-            m_renderWidget->updateDocumentPath();
-            m_renderWidget->setRenderProfile(project->getRenderProperties());
-        }
-        if (m_compositeAction->currentAction()) {
-            m_renderWidget->errorMessage(RenderWidget::CompositeError, m_compositeAction->currentAction()->data().toInt() == 1
-                                                                           ? i18n("Rendering using low quality track compositing")
-                                                                           : QString());
-        }
+    if ( !m_renderWidget && project ) {
+        m_renderWidget = new RenderWidget(project->useProxy(), this);
+        connect(m_renderWidget, &RenderWidget::shutdown, this, &MainWindow::slotShutdown);
+        connect(m_renderWidget, &RenderWidget::selectedRenderProfile, this, &MainWindow::slotSetDocumentRenderProfile);
+        connect(m_renderWidget, &RenderWidget::abortProcess, this, &MainWindow::abortRenderJob);
+        connect(m_renderWidget, &RenderWidget::openDvdWizard, this, &MainWindow::slotDvdWizard);
+        connect(this, &MainWindow::updateRenderWidgetProfile, m_renderWidget, &RenderWidget::adjustViewToProfile);
+        m_renderWidget->setGuides(project->getGuideModel());
+        m_renderWidget->updateDocumentPath();
+        m_renderWidget->setRenderProfile(project->getRenderProperties());
+    }
+    if ( m_renderWidget && m_compositeAction && m_compositeAction->currentAction() ) {
+        m_renderWidget->errorMessage(RenderWidget::CompositeError, m_compositeAction->currentAction()->data().toInt() == 1
+                                                                        ? i18n("Rendering using low quality track compositing")
+                                                                        : QString());
     }
+
     slotCheckRenderStatus();
-    m_renderWidget->show();
+    if ( m_renderWidget ) {
+        m_renderWidget->show();
+    }
     // m_renderWidget->showNormal();
 
     // What are the following lines supposed to do?

src/timeline2/view/timelinecontroller.cpp

@@ -1634,8 +1634,10 @@ bool TimelineController::createSplitOverlay(int clipId, std::shared_ptr<Mlt::Fil
     if (!m_timelinePreview) {
         initializePreview();
     }
-    m_timelinePreview->setOverlayTrack(overlay);
-    m_model->m_overlayTrackCount = m_timelinePreview->addedTracks();
+    if(m_timelinePreview){
+        m_timelinePreview->setOverlayTrack(overlay);
+        m_model->m_overlayTrackCount = m_timelinePreview->addedTracks();
+    }
     return true;
 }
 
@@ -1818,15 +1820,20 @@ void TimelineController::loadPreview(const QString &chunks, const QString &dirty
     for (const QString &frame : qAsConst(dirtyList)) {
         dirtyChunks << frame.toInt();
     }
-    m_disablePreview->blockSignals(true);
-    m_disablePreview->setChecked(enable);
-    m_disablePreview->blockSignals(false);
-    if (!enable) {
-        m_timelinePreview->buildPreviewTrack();
-        m_usePreview = true;
-        m_model->m_overlayTrackCount = m_timelinePreview->addedTracks();
+
+    if ( m_disablePreview ) {
+        m_disablePreview->blockSignals(true);
+        m_disablePreview->setChecked(enable);
+        m_disablePreview->blockSignals(false);
+    }
+    if ( m_timelinePreview ) {
+        if (!enable) {
+            m_timelinePreview->buildPreviewTrack();
+            m_usePreview = true;
+            m_model->m_overlayTrackCount = m_timelinePreview->addedTracks();
+        }
+        m_timelinePreview->loadChunks(renderedChunks, dirtyChunks, documentDate);
     }
-    m_timelinePreview->loadChunks(renderedChunks, dirtyChunks, documentDate);
 }
 
 QMap<QString, QString> TimelineController::documentProperties()

src/titler/graphicsscenerectmove.cpp

@@ -627,7 +627,7 @@ void GraphicsSceneRectMove::mouseReleaseEvent(QGraphicsSceneMouseEvent *e)
     if (m_tool == TITLE_RECTANGLE && (m_selectedItem != nullptr)) {
         setSelectedItem(m_selectedItem);
     }
-    if (m_createdText) {
+    if (m_createdText && m_selectedItem) {
         m_selectedItem->setSelected(true);
         auto *newText = static_cast<MyTextItem *>(m_selectedItem);
         QTextCursor cur(newText->document());