fix: Add null pointer check logic for pointer variables.

1. Some array variable can be declared as const array.
2. Add null pointer check logic for pointer variables.

Author: GongHeng2017

qt/src/Acquirer.cc

@@ -135,9 +135,9 @@ void Acquirer::startScan() {
 	ui.pushButtonScanCancel->setVisible(true);
 	ui.labelScanMessage->setText(_("Starting scan..."));
 
-	double dpi[] = {75.0, 100.0, 200.0, 300.0, 600.0, 1200.0};
-	Scanner::ScanMode modes[] = {Scanner::ScanMode::GRAY, Scanner::ScanMode::COLOR};
-	Scanner::ScanType types[] = {Scanner::ScanType::SINGLE, Scanner::ScanType::ADF_FRONT, Scanner::ScanType::ADF_BACK, Scanner::ScanType::ADF_BOTH};
+	const double dpi[] = {75.0, 100.0, 200.0, 300.0, 600.0, 1200.0};
+	const Scanner::ScanMode modes[] = {Scanner::ScanMode::GRAY, Scanner::ScanMode::COLOR};
+	const Scanner::ScanType types[] = {Scanner::ScanType::SINGLE, Scanner::ScanType::ADF_FRONT, Scanner::ScanType::ADF_BACK, Scanner::ScanType::ADF_BOTH};
 	genOutputPath();
 	QString device = ui.comboBoxScanDevice->itemData(ui.comboBoxScanDevice->currentIndex()).toString();
 	Scanner::Params params = {device, m_outputPath, dpi[ui.comboBoxScanResolution->currentIndex()], modes[ui.comboBoxScanMode->currentIndex()], 8, types[ui.comboBoxScanSource->currentIndex()], 0, 0};

qt/src/Displayer.cc

@@ -281,7 +281,7 @@ bool Displayer::renderImage() {
 		return false;
 	}
 	QImage image = renderer->render(m_currentSource->page, m_currentSource->resolution);
-	if (image.isNull()) {
+	if (image.isNull() || !m_imageItem) {
 		return false;
 	}
 	renderer->adjustImage(image, m_currentSource->brightness, m_currentSource->contrast, m_currentSource->invert);
@@ -536,6 +536,8 @@ void Displayer::wheelEvent(QWheelEvent* event) {
 
 QPointF Displayer::mapToSceneClamped(const QPoint& p) const {
 	QPointF q = mapToScene(p);
+	if (!m_imageItem)
+		return q;
 	QRectF bb = m_imageItem->sceneBoundingRect();
 	q.rx() = std::min(std::max(bb.x(), q.x()), bb.x() + bb.width());
 	q.ry() = std::min(std::max(bb.y(), q.y()), bb.y() + bb.height());