GH-1556 do not crash when instance has no update task while creating an instance

application/MainWindow.cpp

@@ -1185,7 +1185,10 @@ void MainWindow::finalizeInstance(InstancePtr inst)
 					QString error = QString("Instance load failed: %1").arg(reason);
 					CustomMessageBox::selectable(this, tr("Error"), error, QMessageBox::Warning)->show();
 				});
-		loadDialog.execWithTask(update.get());
+		if(update)
+		{
+			loadDialog.execWithTask(update.get());
+		}
 	}
 	else
 	{

application/dialogs/ProgressDialog.cpp

@@ -17,6 +17,7 @@
 #include "ui_ProgressDialog.h"
 
 #include <QKeyEvent>
+#include <QDebug>
 
 #include "tasks/Task.h"
 
@@ -57,6 +58,12 @@ int ProgressDialog::execWithTask(Task *task)
 	this->task = task;
 	QDialog::DialogCode result;
 
+	if(!task)
+	{
+		qDebug() << "Programmer error: progress dialog created with null task.";
+		return Accepted;
+	}
+
 	if(handleImmediateResult(result))
 	{
 		return result;