Got the error part thanks

I'll update my code:

.h File:
Qt Code: 
  1. #ifndef MINECRAFTSKINDOWNLOADER_H
  2. #define MINECRAFTSKINDOWNLOADER_H
  3.  
  4. #include <QMainWindow>
  5. #include <QtNetwork/QNetworkReply>
  6. #include <QtNetwork/QNetworkAccessManager>
  7.  
  8. namespace Ui {
  9. class MinecraftSkinDownloader;
  10. }
  11.  
  12. class MinecraftSkinDownloader : public QMainWindow
  13. {
  14.     Q_OBJECT
  15.  
  16. public:
  17.     explicit MinecraftSkinDownloader(QWidget *parent = 0);
  18.     ~MinecraftSkinDownloader();
  19.     QByteArray pngData;
  20.     QNetworkAccessManager *manager;
  21.  
  22. private slots:
  23.  
  24.     void slot_netwManagerFinished(QNetworkReply *reply);
  25.  
  26.     void onsaveAs_clicked();
  27.  
  28.     void on_clear_clicked();
  29.  
  30.     void on_pushButton_clicked();
  31.  
  32. private:
  33.     Ui::MinecraftSkinDownloader *ui;
  34.  
  35.  
  36. };
  37.  
  38. #endif // MINECRAFTSKINDOWNLOADER_H
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.cpp File
Qt Code: 
  1. #include "minecraftskindownloader.h"
  2. #include "ui_minecraftskindownloader.h"
  3. #include <QWidget>
  4. #include <QObject>
  5. #include <QtNetwork/QNetworkAccessManager>
  6. #include <QFileDialog>
  7. #include <QtNetwork/QNetworkRequest>
  8. #include <QDebug>
  9. #include <QUrl>
  10. #include <QFile>
  11. #include <QPixmap>
  12. #include <QMessageBox>
  13.  
  14. MinecraftSkinDownloader::MinecraftSkinDownloader(QWidget *parent) :
  15.     QMainWindow(parent),
  16.     ui(new Ui::MinecraftSkinDownloader)
  17. {
  18.     ui->setupUi(this);
  19.     this->setWindowTitle("Minecraft Skin Downloader");
  20.     QIcon icon(":/ico");
  21.     setWindowIcon(icon);
  22.     setFixedSize(400, 200);
  23.     setStyleSheet("QMainWindow { background-image: url(:/bg.png); } ");
  24.  
  25.     connect(ui->save, SIGNAL(clicked()), this, SLOT(onsaveAs_clicked()));
  26.  
  27. }
  28.  
  29. MinecraftSkinDownloader::~MinecraftSkinDownloader()
  30. {
  31.     delete ui;
  32. }
  33.  
  34. //http://s3.amazonaws.com/MinecraftSkins/USERNAMEHERE.png
  35.  
  36. void MinecraftSkinDownloader::on_pushButton_clicked()
  37. {
  38.     QString prefix = "http://s3.amazonaws.com/MinecraftSkins/";
  39.     QString usrl = prefix += ui->lineEdit->text() += ".png";
  40.  
  41.     //QNetworkAccessManager *manager = new QNetworkAccessManager(this);
  42.     connect(manager, SIGNAL(finished(QNetworkReply*)), this, SLOT(slot_netwManagerFinished(QNetworkReply*)));
  43.  
  44.     QUrl url(usrl);
  45.     QNetworkRequest request(url);
  46.  
  47.     manager->get(request);
  48.  
  49. }
  50.  
  51. void MinecraftSkinDownloader::slot_netwManagerFinished(QNetworkReply *reply)
  52. {
  53.  
  54.     if (reply->error() != QNetworkReply::NoError)
  55.     {
  56.         qDebug() << "Error in" << reply->url() << ":" << reply->errorString();
  57.         QPixmap noUsr(":/voidUser.png"); // Void User path
  58.         ui->preview->show();
  59.         ui->preview->setStyleSheet("background: transparent;");
  60.         ui->preview->setPixmap(noUsr);
  61.         reply->deleteLater();
  62.         return;
  63.     }
  64.  
  65.     pngData = reply->readAll();
  66.     QPixmap pixmap;
  67.     pixmap.loadFromData(pngData);
  68.     QPixmap scaled = pixmap.scaled(128,64,Qt::IgnoreAspectRatio, Qt::FastTransformation);
  69.     ui->preview->show();
  70.     ui->preview->setStyleSheet("QLabel { background-color: white; }");
  71.     ui->preview->setPixmap(scaled);
  72.     reply->deleteLater();
  73.  
  74. }
  75.  
  76. void MinecraftSkinDownloader::onsaveAs_clicked()
  77. {
  78.     if(pngData.isEmpty())
  79.     {
  80.         ui->preview->show();
  81.         QPixmap error(":/noSaveData.png");
  82.         ui->preview->setPixmap(error);
  83.         return;
  84.     }
  85.  
  86.     QString filename = QFileDialog::getSaveFileName(this, tr("Save Skin"), "C:/Users/", ("PNG Image (*.png)"));
  87.  
  88.     QFile file(filename);
  89.     file.open(QIODevice::WriteOnly);
  90.     file.write(pngData);
  91.     file.close();
  92. }
  93.  
  94. void MinecraftSkinDownloader::on_clear_clicked()
  95. {
  96.     pngData.clear();
  97.     ui->preview->setStyleSheet("background: transparent;");
  98.     ui->lineEdit->clear();
  99.     ui->preview->hide();
  100.     return;
  101. }
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It crashes the moment I press that on_pushButton_clicked(), and doesn't even get to display the error message (voidUser.png) when I leave it blank. Same thing happens when I put a valid username in there too.