[partition] Update waiting widget only if it (still) exists

src/modules/partition/PartitionViewStep.cpp

@@ -51,7 +51,7 @@ PartitionViewStep::PartitionViewStep( QObject* parent )
 
     m_waitingWidget = new WaitingWidget( QString() );
     m_widget->addWidget( m_waitingWidget );
-    CALAMARES_RETRANSLATE( m_waitingWidget->setText( tr( "Gathering system information..." ) ); );
+    CALAMARES_RETRANSLATE( if (m_waitingWidget) {  m_waitingWidget->setText( tr( "Gathering system information..." ) ); } );
 
     m_core = new PartitionCoreModule( this );  // Unusable before init is complete!
     // We're not done loading, but we need the configuration map first.