Fix some Coverity use-after-free warnings

(cherry-picked from eb39579)

Author: nyalldawson

src/app/qgisapp.cpp

@@ -7368,8 +7368,10 @@ QgsLayoutDesignerDialog *QgisApp::createNewPrintLayout( const QString &t )
   QgsPrintLayout *layout = new QgsPrintLayout( QgsProject::instance() );
   layout->setName( title );
   layout->initializeDefaults();
-  QgsProject::instance()->layoutManager()->addLayout( layout );
-  return openLayoutDesignerDialog( layout );
+  if ( QgsProject::instance()->layoutManager()->addLayout( layout ) )
+    return openLayoutDesignerDialog( layout );
+  else
+    return nullptr;
 }
 
 QgsLayoutDesignerDialog *QgisApp::createNewReport( QString title )

src/core/processing/models/qgsprocessingmodelalgorithm.cpp

@@ -961,8 +961,8 @@ bool QgsProcessingModelAlgorithm::activateChildAlgorithm( const QString &id )
 
 void QgsProcessingModelAlgorithm::addModelParameter( QgsProcessingParameterDefinition *definition, const QgsProcessingModelParameter &component )
 {
-  addParameter( definition );
-  mParameterComponents.insert( definition->name(), component );
+  if ( addParameter( definition ) )
+    mParameterComponents.insert( definition->name(), component );
 }
 
 void QgsProcessingModelAlgorithm::updateModelParameter( QgsProcessingParameterDefinition *definition )