jfjoch_viewer: fix error in updating the pixmap

viewer/image_viewer/JFJochImage.cpp

@@ -596,9 +596,7 @@ void JFJochImage::Redraw() {
 }
 
 void JFJochImage::GeneratePixmap() {
-    // Reuse buffer if size matches, otherwise reallocate
-    if (qimg_buffer_.width() != int(W) || qimg_buffer_.height() != int(H))
-        qimg_buffer_ = QImage(int(W), int(H), QImage::Format_RGB32);
+    QImage qimg(int(W), int(H), QImage::Format_RGB32);
 
     image_rgb.resize(W * H);
 
@@ -632,7 +630,7 @@ void JFJochImage::GeneratePixmap() {
     for (int y = 0; y < H; ++y) rows.push_back(y);
 
     QtConcurrent::blockingMap(rows, [&](int y) {
-        QRgb *scanLine = reinterpret_cast<QRgb*>(qimg_buffer_.scanLine(y));
+        QRgb *scanLine = reinterpret_cast<QRgb*>(qimg.scanLine(y));
         const float *row = &image_fp[y * W];
         rgb *out = &image_rgb[y * W];
 
@@ -673,7 +671,7 @@ void JFJochImage::GeneratePixmap() {
         }
     });
 
-    pixmap = QPixmap::fromImage(qimg_buffer_);
+    pixmap = QPixmap::fromImage(qimg);
     pixmap.setDevicePixelRatio(1.0);
 }